Pharmacokinetic properties of a novel formulation of S-adenosyl-L-methionine phytate.

S-adenosyl-L-methionine (SAM), the main endogenous methyl donor, is the adenosyl derivative of the amino acid methionine, which displays many important roles in cellular metabolism. It is widely used as a food supplement and in some countries is also marketed as a drug. Its interesting nutraceutical and pharmacological properties prompted us to evaluate the pharmacokinetics of a new form of SAM, the phytate salt. The product was administered orally to rats and pharmacokinetic parameters were evaluated by comparing the results with that obtained by administering the SAM tosylated form (SAM PTS). It was found that phytate anion protects SAM from degradation, probably because of steric hindrance exerted by the counterion, and that the SAM phytate displayed significant better pharmacokinetic parameters compared to SAM PTS. These results open to the perspective of the use of new salts of SAM endowed with better pharmacokinetic properties.

Human cystathionine ß-synthase (CBS) contains two classes of binding sites for S-adenosylmethionine (SAM): complex regulation of CBS activity and stability by SAM.

CBS (cystathionine ß-synthase) is a multidomain tetrameric enzyme essential in the regulation of homocysteine metabolism, whose activity is enhanced by the allosteric regulator SAM (S-adenosylmethionine). Missense mutations in CBS are the major cause of inherited HCU (homocystinuria). In the present study we apply a novel approach based on a combination of calorimetric methods, functional assays and kinetic modelling to provide structural and energetic insight into the effects of SAM on the stability and activity of WT (wild-type) CBS and seven HCU-causing mutants. We found two sets of SAM-binding sites in the C-terminal regulatory domain with different structural and energetic features: a high affinity set of two sites, probably involved in kinetic stabilization of the regulatory domain, and a low affinity set of four sites, which are involved in the enzyme activation. We show that the regulatory domain displays a low kinetic stability in WT CBS, which is further decreased in many HCU-causing mutants. We propose that the SAM-induced stabilization may play a key role in modulating steady-state levels of WT and mutant CBS in vivo. Our strategy may be valuable for understanding ligand effects on proteins with a complex architecture and their role in human genetic diseases and for the development of novel pharmacological strategies.

A study to enhance the oral bioavailability of s-adenosyl-l-methionine (SAMe): SLN and SLN nanocomposite particles.

The endogenous molecule, S-adenosyl-l-methionine (SAMe) is a key factor due to its role in the methylation cycle and modulation of monoaminergic neurotransmission. Since many mental disorders have linked to the monoaminergic system, the level of SAMe in blood and cerebrospinal fluid is important in the treatment of major depression. In this study, solid lipid nanoparticles (SLN) were prepared in order to increase the limited oral bioavailability of SAMe, and SLN based nanocomposite particles (SAMe-SLN-NC) were further developed using an enteric polymer for passive targeting of intestinal lymphatic system. In this manner, it was also aimed to protect SAMe loaded SLN from harsh gastric environment as well as hepatic first-pass metabolism. Dynamic light scattering (DLS) analysis of SLN was performed, drug content was measured, SAMe release patterns were examined and the permeation ability of SAMe was investigated by the Parallel Artificial Membrane Permeability Assay (PAMPA) to characterize SAMe loaded SLN formulation. According to the PAMPA results, SAMe-SLN with the average particle size of 242 nm showed enhanced SAMe permeability in comparison to pure drug. Delayed drug release obtained by SLN nanocomposite particles indicated the protection of drug-loaded SLN in the acidic gastric medium and their intact presence in the intestine. SAMe solution or particle suspensions were prepared using 0.45 (w/v) hydroxypropyl methylcellulose aqueous solution to be applied to groups of animals for pharmacokinetic studies. In vivo pharmacokinetic parameters revealed enhancement in relative bioavailability of SAMe upon oral administration of SLN based formulations. This was attributed to intact absorption of lipid matrix through lymphatic path. A statistically significant increase in SAMe plasma levels was obtained at 15th and 30th minutes with SAMe-SLN and at 2nd and 4th hours with SAMe-SLN-NC. Overall results suggest that SLN is a promising carrier to passive lymphatic targeting of SAMe and novel SLN nanocomposite particles which presented efficient oral bioavailability is a potential way for oral delivery of SAMe and treatment of major depression.

Pharmacokinetic study of a novel oral formulation of S-adenosylmethionine (MSI-195) in healthy subjects: dose escalation, food effect and comparison to a commercial nutritional supplement product.

BACKGROUND: A novel, high bioavailability oral, enteric coated tablet formulation of S-adenosylmethionine (MSI-195) has been developed for life science application. The present research reports on a Phase 1 study to (i) determine the safety of single doses of MSI-195 (ii) to determine the dose proportionality of MSI-195 at doses of 400, 800 and 1600 mg (iii) determine the pharmacokinetics of MSI-195 compared with a commercial reference product (SAM-e Complete™) over 24 h and (iv) to determine the effect of food on the pharmacokinetic profile of MSI-195 in human subjects. METHODS: This study was a pharmacokinetic and safety evaluation of MSI-195 and a commercial comparator broken into two stages. The first stage was an exploratory single ascending dose design of MSI-195 in 8 healthy normal male volunteers. The second stage was a single dose evaluation, targeting 26 male and female volunteers at set doses of MSI-195 and commercial comparator in a cross-over design followed by a food effect study on MSI-195. Plasma samples were collected and assayed for S-adenosylmethionine using a validated HPLC method with MS/MS detection. The main absorption and disposition parameters were calculated using a non-compartmental approach with a log-linear terminal phase assumption. Statistical analysis was based on an ANOVA model or t test as appropriate. RESULTS: MSI-195 was found to be generally well tolerated with an adverse event profile similar to the SAM-e Complete™ comparator product. The relative bioavailability of MSI-195 was approximately 2.8-fold higher than SAM-e Complete based on area under the curve (AUC) ratios for the two products and the MSI-195 formulation exposure based on AUC was found to be approximately dose proportional. There was a significant food effect for MSI-195 with a delayed time to maximum absorption Tmax, going from 4.5 h under fasted conditions to 13 h under fed conditions, and area under the curve with food reduced to 55% of that seen under fasting conditions. CONCLUSIONS: The overall conclusion was that MSI-195 was well tolerated and has markedly higher bioavailability compared with both the SAM-e Complete™ commercial product tested and, on a per mg basis, products reported in other literature. TRIAL REGISTRATION: ClinicalTrials.gov, identifier NCT04623034 . Retrospectively registered Nov 9, 2020.

Pharmacokinetic properties of S-adenosylmethionine after oral and intravenous administration of its tosylate disulfate salt: a multiple-dose, open-label, parallel-group study in healthy Chinese volunteers.

BACKGROUND: S-adenosylmethionine (SAMe) is an endogenous molecule that plays an important role in cellular metabolism. Despite being widely used as a dietary supplement with claimed benefits for numerous conditions, there is little information about the pharmacokinetic properties of exogenous SAMe. OBJECTIVES: One aim of this study was to characterize the pharmacokinetic properties of SAMe after administration of single and multiple doses of orally and intravenously administered SAMe tosylate disulfate (STD) in healthy male and female Chinese volunteers. Because men have higher erythrocyte levels of endogenous SAMe than do women, we also assessed the effects of sex on the disposition of SAMe. METHODS: A simple and sensitive assay for SAMe based on liquid chromatography-mass spectrometry using selected-ion monitoring of analyte and acyclovir as internal standard was developed and validated. The assay was used to study the pharmacokinetic properties of SAMe. STD was administered as single and multiple doses of enteric-coated tablets and IV infusion of STD to groups of healthy native Chinese volunteers. After an overnight fast, male and female Chinese volunteers were assigned to receive STD 1000 mg for 5 days, either in enteric-coated tablet formulation or as a 250-mL IV infusion. Blood samples were collected 24 hours after the first and last dose and used for determining plasma SAMe concentrations and pharmacokinetic parameters. For the oral formulation, SAMe concentrations were corrected for concentrations of endogenous SAMe. Pharmacokinetic parameters were calculated for men and women separately and for the total group of volunteers. Adverse events were monitored using a physician during blood collection and by spontaneous reporting. RESULTS: Twenty healthy volunteers were enrolled (oral formulation: 5 men, 5 women; mean [SD] age, 24.1 [4.7] years [range, 21-37 years]; mean [SD] weight, 59.9 [4.8] kg [range, 54-70 kg]; IV formulation: 5 men, 5 women; mean [SD] age, 22.6 [1.8] years [range, 21-27 years]; mean [SD] weight, 59.5 [5.4] kg [range, 53-67 kg]). None of the between-sex differences in SAMe pharmacokinetic properties were significant. The (mean [SD]) pharmacokinetic properties of singledose oral SAMe in men and women, respectively, were as follows: C(max), 2.37 (1.58) and 2.50 (1.83) micromol/L; T(max), 5.40 (1.14) and 5.20 (1.48) hours; AUC(0-24), 8.56 (5.16) and 10.3 (8.0) micromol/L/h; and t(1/2beta), 6.06 (1.80) and 6.28 (2.60) hours. Corresponding values with the single-dose IV formulation were: C(max), 127 (49) and 211 (94) micromol/L; T(max), 1.90 (0.22) and 1.60 (0.22) hours; AUC(0-24), 329 (84) and 480 (176) micromol/L/h; and t(1/2beta), 4.34 (0.57) and 3.83 (0.78) hours. The single-dose oral:IV ratios of AUC(0-24) in men and women, respectively, were 2.60% and 2.14% (degrees of fluctuation: 4.96 [1.77] and 9.49 [0.91]). The pharmacokinetic properties of multiple-dose oral and IV SAMe were not significantly different from those with single-dose administration. None of the volunteers reported any adverse events during the study. CONCLUSIONS: In this small study in healthy Chinese volunteers, there were no significant differences in the pharmacokinetic parameters of SAMe between men and women or between single- and multiple-dose administration of STD 1000 mg administered orally or intravenously. No evidence of accumulation of SAMe in plasma was found on multiple dosing. Both enteric-coated tablets and the IV infusion were well tolerated in these volunteers.

Double-blind, placebo-controlled pharmacodynamic studies with a nutraceutical and a pharmaceutical dose of ademetionine (SAMe) in elderly subjects, utilizing EEG mapping and psychometry.

In a double-blind, placebo-controlled crossover study, the effects of S-adenosyl-l-methionine (SAMe) on brain function measures of 12 normal elderly volunteers (6 m/6 f, aged 57-73 years, mean: 61 years) were investigated by means of EEG mapping and psychometry. In random order, the subjects were orally administered a pharmaceutical dose of 1600 mg SAMe, a nutraceutical dose of 400 mg SAMe and placebo, each over a period of 15 days, with wash-out periods of 2 weeks in between. EEG recordings, psychometric tests and evaluations of tolerability and side effects were carried out 0, 1, 3 and 6 h after drug administration on days 1 and 15. Multivariate analysis based on MANOVA/Hotelling T2 tests of quantitative EEG data demonstrated significant central effects of SAMe as compared with placebo after acute, subacute and superimposed drug administration of both the nutraceutical and the pharmaceutical dose. EEG changes induced by SAMe were characterized by an increase in total power, a decrease in absolute and relative power in the delta/theta and slow alpha frequencies, an increase in absolute and relative power in the alpha-2 and beta frequencies as well as an acceleration of the alpha centroid and the centroid of the total power spectrum. The delta/theta and the beta centroid showed variable changes over time. The dominant alpha frequency was accelerated, the absolute and relative power in the dominant alpha frequency attenuated after SAMe as compared with placebo. These acute and subacute pharmaco-EEG findings in elderly subjects are typical of activating antidepressants. Time-efficacy calculations showed that acute oral administration of SAMe in both the nutraceutical and the pharmaceutical dose induced the pharmacodynamic peak effect in the first hour with a subsequent decline. The 3rd and 6th hours still showed a significant encephalotropic effect after the 1600 mg dose. The maximum EEG effect was noted after 2 weeks of oral administration of both 1600 mg/die and 400 mg/die. The superimposed dose induced significant encephalotropic effects in the 3rd hour after 400 mg and in the 3rd and 6th hours after 1600 mg as compared with pre-treatment. Dose-efficacy calculations showed that the pharmaceutical dose of 1600 mg had a more pronounced effect on the CNS than the nutraceutical dose of 400 mg, with both doses being superior to placebo. Psychometric tests concerning noopsychic and thymopsychic measures as well as critical flicker fusion frequency generally demonstrated a lack of differences between SAMe and placebo, which reflects a good tolerability of the drug in elderly subjects. This was corroborated by the findings on side effects, pulse and blood pressure.

S-adenosyl-L-methionine: transcellular transport and uptake by Caco-2 cells and hepatocytes.

S-adenosyl-L-methionine (SAMe) is an endogenous molecule that is known to be protective against hepatotoxic injury. Although oral SAMe appears to be absorbed across the intestinal mucosa, its systemic bioavailability is low. The reason for this is unknown. Using the Caco-2 cell culture model for enterocyte absorption, we determined the mode by which SAMe is transported across this cell monolayer. We also determined the extent it is taken up by both Caco-2 cells and hepatocytes. In Caco-2 cells transport was observed in both apical to basolateral and basolateral to apical directions. The apparent permeability coefficients (Papp) appeared to be concentration independent and were similar in both directions (0.7x10(-6) and 0.6x10(-6) cm s-1, respectively), i.e. identical to that of the paracellular transport marker mannitol (0.9x10(-6) and 0.7x10(-6) cm s-1). This mode of transport was supported by a four-fold increase in the Papp for SAMe transport in Ca++-free buffer. Cellular uptake of SAMe was examined in both Caco-2 cells and cultured rat hepatocytes. Uptake by hepatocytes was not saturable in a concentration range of 0.001-100 microM. Accumulation by both cell types was very low, with a cell:medium ratio at equilibrium of only 0.2-0.5. This low cell accumulation supports the finding of paracellular transport as the only mode of cell membrane transport. Increased hepatocellular protection for SAMe may be accomplished by converting SAMe to a more lipid-soluble prodrug.

Evaluation of the influence of S-adenosylmethionine on systemic and hepatic effects of prednisolone in dogs.

OBJECTIVE: To evaluate the influence of a 1,4-butanedisulfonate stable salt of S-adenosylmethionine (SAMe) administered orally on clinicopathologic and hepatic effects induced by long-term administration of prednisolone in dogs. ANIMALS: 12 healthy dogs. PROCEDURE: Following a pilot study (4 dogs), 2 groups of 4 dogs received prednisolone (2.2 mg/kg) orally once daily (84-day trial). One group received SAMe (20 mg/kg/d divided in 2 doses) for 42 days and then a placebo for 42 days; the other group received treatments in the reverse order. Before and during the trial, numerous variables were monitored, including serum total alkaline phosphatase (ALP) and glucocorticoid-induced ALP (G-ALP) activities, serum haptoglobin concentration, and total and oxidized glutathione (TGSH and GSSG) and thiobarbiturate-reacting substances (TBARS) concentrations in erythrocytes and liver tissue (days 0, 42, and 84). Hepatic specimens also were examined microscopically. RESULTS: The stable salt of SAMe was biologically available; plasma concentrations of SAMe or prednisolone were not affected by coadministration. Compared with baseline values, serum ALP and G-ALP activities and haptoglobin concentrations increased and erythrocyte GSSG and TBARS concentrations decreased with both treatments. Erythrocyte TGSH concentration decreased with the prednisolone-placebo treatment. Administration of SAMe appeared to conserve erythrocyte TGSH values and did not inhibit hepatocyte glycogen vacuolation but increased hepatic TGSH concentration and improved the hepatic tissue GSSG:TGSH ratio. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, administration of 20 mg of SAMe/kg/d may mitigate the apparent pro-oxidant influences of prednisolone but did not block development of classic clinicopathologic or histologic features of vacuolar hepatopathy.

Effects of the disruption of transmethylation in the central nervous system: an animal model.

INTRODUCTION: Central nervous system (CNS) methyltransferases methylate a wide range of substrates including proteins, lipids, nucleic acids and hormones. In every instance the methyl donor is S-adenosylmethionine (SAMe) and the demethylated product is S-adenosylhomocysteine (SAH). Methylation can be disrupted when there is an inadequate supply of methionine synthase (following vitamin B12 deficiency or folate deficiency), SAMe synthetase (due to ethanol), or SAH hydrolase (for unknown reasons). MATERIAL AND METHODS: 5-week-old pigs were maintained in an environment of either air or nitrous oxide, which inhibits methionine synthase, and were fed either a methionine-unsupplemented or methionine-enriched diet. After 3 to 10 weeks, pigs were killed by pentobarbitone injection and the levels of methionine and SAMe in the pigs' brain, spinal cord, plasma, liver, and kidney assessed. RESULTS: Pigs maintained in nitrous oxide displayed a dramatic fall in methionine levels in plasma and brain tissues but maintained relatively normal SAMe levels in these tissues. Brain and spinal cord cystathionine levels were markedly elevated, especially in those animals receiving oral methionine, as in the absence of methionine synthase homocysteine can be metabolized only through the catabolic pathway to cystathionine and cysteine. CONCLUSION: Disorders such as vitamin B12 deficiency or folate deficiency inhibit methylation by limiting the availability of SAMe or by elevating levels of the inhibitor SAH. In either case, the disruption of a wide range of methylation reactions can cause clinical sequelae ranging from structural abnormalities such as myelopathy to functional abnormalities such as depression.

S-adenosylmethionine levels in psychiatric and neurological disorders: a review.

INTRODUCTION: S-adenosylmethionine (SAMe) is an important methyl donor in over 35 methylation reactions involving DNA, proteins, phospholipids and catechol- and indole- amines. MATERIAL AND METHODS: This article reviews the studies that have examined brain and blood levels of SAMe in several psychological, neurological and metabolic disorders. RESULTS: Although studies have found no consistent changes in whole blood SAMe levels in psychiatric patients, other investigators have found low cerebrospinal fluid (CSF) SAMe levels in patients with neurological disorders such as Alzheimer's dementia, subacute combined degeneration of the spinal cord (SACD), and HIV-related neuropathies, as well as in patients with metabolic disorders such as 5, 10-CH2-H4 folate reductase deficiency. CONCLUSION: Intravenous or oral administration of SAMe thus represents a possible treatment for these neurological and metabolic disorders.

S-adenosyl-L-methionine: effects on brain bioenergetic status and transverse relaxation time in healthy subjects.

BACKGROUND: S-adenosyl-L-methionine is an effective treatment for clinical depression, although the mechanism underlying this effect is unclear. Presently, in vivo phosphorus magnetic resonance spectroscopy (31P MRS) and brain transverse relaxometry were employed to test if S-adenosyl-L-methionine supplementation alters brain bioenergetics and/or transverse relaxation time (T2RT) in a nondepressed cohort. If these magnetic resonance techniques are sensitive to S-adenosyl-L-methionine induced alterations in neurochemical processes, these methods may be used in cases of clinical depression to elucidate the mechanism underlying the antidepressant effect of S-adenosyl-L-methionine. METHODS: Twelve subjects self-administered 1600 mg of oral S-adenosyl-L-methionine daily. Phosphorus spectra and transverse relaxation time were acquired at baseline and after treatment using a 1.5 Tesla scanner. RESULTS: Phosphocreatine levels were significantly higher after treatment, whereas beta nucleoside triphosphate levels, predominantly adenosine triphosphate in brain, were significantly lower after treatment. A surprising gender difference in T2RT emerged after supplementation, with women exhibiting significantly lower T2RT than men. CONCLUSIONS: Alterations in phosphocreatine and beta nucleoside triphosphate are consistent with the report that S-adenosyl-L-methionine is involved in the production of creatine, which in turn is phosphorylated to phosphocreatine using adenosine triphosphate. These findings suggest that S-adenosyl-L-methionine alters parameters associated with cerebral bioenergetic status and that some effects of S-adenosyl-L-methionine (T2RT) occur in a gender-specific manner.

Isolation and characterisation of 5'-fluorodeoxyadenosine synthase, a fluorination enzyme from Streptomyces cattleya.

5'-fluorodeoxyadenosine synthase, a C-F bond-forming enzyme, has been purified from Streptomyces cattleya. The enzyme mediates a reaction between inorganic fluoride and S-adenosyl-L-methionine (SAM) to generate 5'-fluoro-5'-deoxyadenosine. The molecular weight of the monomeric protein is shown to be 32.2 kDa by electrospray mass spectrometry. The kinetic parameters for SAM (K(m) 0.42 mM, V(max) 1.28 U/mg) and fluoride ion (K(m) 8.56 mM, V(max) 1.59 U/mg) have been evaluated. Both S-adenosyl-L-homocysteine (SAH) and sinefungin were explored as inhibitors of the enzyme. SAH emerged as a potent competitive inhibitor (K(i) 29 microM) whereas sinefungin was only weakly inhibitory.

S-Adenosyl-L-methionine (SAMe): from the bench to the bedside--molecular basis of a pleiotrophic molecule.

S-Adenosyl-L-methionine (SAMe), a metabolite present in all living cells, plays a central role in cellular biochemistry as a precursor to methylation, aminopropylation, and transsulfuration pathways. As such, SAMe has been studied extensively since its chemical structure was first described in 1952. Decades of research on the biochemical and molecular roles of SAMe in cellular metabolism have provided an extensive foundation for its use in clinical studies, including those on depression, dementia, vacuolar myelopathy, liver disease, and osteoarthritis. This article provides an overview of the biochemical, molecular, and therapeutic effects of this pleiotrophic molecule.

S-adenosylmethionine and affective disorder.

Several open and double-blind studies suggest that SAMe may have an anti-depressant effect, and further studies are indicated. SAMe may exert a beneficial effect selectively on endogenous rather than neurotic depression. SAMe crosses the blood-brain barrier. SAMe is involved in several central enzyme pathways relating to transmethylation and folate and monoamine metabolism as well as in membrane function and neuro-transmission. The neuropharmacology of SAMe's effect on mood and the switch mechanism has yet to be fully explored. The actions of SAMe on the dopaminergic system are as yet unclear. SAMe is a physiologic substance that is non-toxic and relatively free of severe side effects (with the exception of mania, which may be a manifestation of the basic mood disorder.

Pharmacologic aspects of S-adenosylmethionine. Pharmacokinetics and pharmacodynamics.

Several studies in animals have shown the efficacy of parenteral S-adenosylmethionine (SAMe) as an anti-inflammatory drug. In this article, data are reported on plasma kinetics, distribution, and metabolism of SAMe after oral administration since preference is given to oral dosage in the usual clinical practice. The results demonstrate the intestinal absorption of SAMe and its active metabolism. Experiments confirm the anti-inflammatory activity of the drug by the oral route. Results are also reported on the analgesic effect of SAMe.

Neuropharmacology of S-adenosyl-L-methionine.

The metabolite S-adenosyl-L-methionine (SAMe), when prepared as the stable p-toluene-sulfonate complex of its sulfate salt and given parenterally in high doses, appears to have mood-elevating effects in depressed adults. The material is remarkably well tolerated when given by injection or intravenous infusion for this purpose, even in elderly or demented patients. Assuming that the toluene sulfonate component is inert, SAMe appears to have central neuropharmacologic effects after systemic injection in high doses. Nevertheless, the functional consequences of these remain unclear and, indeed, the ability of exogenous SAMe to reach the brain, and especially neuronal cytoplasm, is limited. SAMe has small effects on monoamine metabolism and, after injection, appears to have effects on the microviscosity of cell membranes that may be related to stimulation of phospholipid synthesis. The recent introduction of an orally administered form of SAMe for use in the treatment of osteoarthritis promises to stimulate further study of SAMe in disease-associated depression, major depressive disorder, and other neuropsychiatric conditions.

Metabolism of exogenous S-adenosyl-L-methionine in patients with liver disease.

S-Adenosyl-L-methionine (SAMe) is an important methyl group donor for many biochemical reactions. It is widespread in body tissues, including the liver, and is metabolised via 3 main metabolic pathways: transmethyltion, trans-sulphuration and amino-propylation. In chronic liver disease these pathways are impaired, the major abnormality being a reduction in SAMe-synthetase activity. Exogenous SAMe may overcome the effects of impaired SAMe-synthetase activity. Exogenous SAMe is stable in digestive juices and, although well absorbed orally, bioavailability is reduced because of a significant first pass effect in the liver. Dose-dependent peak plasma levels are achieved within 3 to 6 hours of oral administration and plasma levels approach baseline after 24 hours. Volumes of distribution are small. The metabolism of exogenous SAMe appears to follow the known pathways of endogenous SAMe metabolism and the initial data suggest that the process is largely unaffected in patients with chronic liver disease.

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.

The inhibitory role of methylation on the binding characteristics of dopamine receptors and transporter.

Excess methylation has been suggested to play a role in the pathogenesis of Parkinson's disease (PD), since the administration of S-adenosylmethionine (SAM), a biological methyl donor, induces PD-like changes in rodents. It was proposed that SAM-induced PD-like changes might be associated with its ability to react with the dopaminergic system. In the present study the effects of SAM on dopamine receptors and transporters were investigated using rats and cloned dopamine receptor proteins. Autoradiographic examination of SAM indicated its tendency to be localized and accumulated in rat striatal region after the intracerebroventricular injection into rat brain. Moreover, results showed that SAM significantly decreased dopamine D1 and D2 receptor binding activities by decreasing the Bmax and increasing the Kd values. At concentrations of 0.1, 0.25 and 0.5 mM, SAM was able to reduce the Bmax from the control value of 848.1 for dopamine D1-specific ligand [3H] SCH 23390 to 760.1, 702.6 and 443.0 fmol/mg protein, respectively. At the same concentrations, SAM was able to increase the Kd values from 0.91 for the control to 1.06, 3.84 and 7.01 nM of [3H] SCH 23390, respectively. The effects of SAM on dopamine D2 binding were similar to those of dopamine D1 binding. SAM also decreased dopamine transporter activity. The interaction of SAM with dopamine receptor proteins produced methanol from methyl-ester formation and hydrolysis. We propose that the SAM effect might be related to its ability to react with dopamine receptor proteins through methyl-ester formation and methanol production following the hydrolysis of the carboxyl-methylated receptor proteins.