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Biomedical subjects

E Shohami

Publications and source records attributed to E Shohami.

16 recordsLinked to original sources
PubMed1992

Changes in brain polyamine levels following head injury.

The changes in polyamines levels in the brain after closed head injury were studied in rats. At 1 and 15 min, 24 and 48 h after closed head injury cortical tissue from the site of injury, from the contralateral region, and from remote areas were taken. The levels of the diamine putrescine and the polyamines spermine and spermidine were assayed by thin layer liquid chromatography of their dansyl derivatives. Head injury induced a significant increase in putrescine at 48 h at the site of injury and in the frontal lobe of the injured hemisphere, respectively. In the contralateral hemisphere only minor changes in putrescine were found. Spermine and spermidine showed minor changes at that time course. We have previously shown that at 24-48 h after injury, severe edema is found at the site injury. In order to study the role of putrescine in edema formation in this model we treated the traumatized rats with alpha-difluoromethyl-ornithine (DFMO), an inhibitor of ornithine-decarboxylase, the rate limiting enzyme in putrescine biosynthesis. This drug did not affect the level of edema 4 or 48 h after injury although it abolished the increase in putrescine. The effect of DFMO on blood-brain barrier function was studied, using Evans blue extravasation, at the early post-traumatic period (15 min-4 h), where a massive amount of dye is taken up by traumatized brain. No changes in the amount of dye extracted was found after DFMO treatment. On the other hand, DFMO had a beneficial effect on the neurological outcome, as evaluated by a set of clinical criteria.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Glucocorticoid regulation of eicosanoid production by glial cells under basal and stimulated conditions.

We measured the production of two eicosanoids, prostaglandin E2 and thromboxane-B2, by rat glial cell cultures under basal conditions, following stimulation with phorbol-12-myristate-13-acetate and the bacterial endotoxin lipopolysaccharide, and following treatment with synthetic glucocorticoids. Stimulation of rat glial cells in culture with either phorbol-12-myristate-13-acetate or lipopolysaccharide caused a 1.5-5.0-fold increase in prostaglandin E2 production, but did not affect thromboxane production. Pretreatment of the cultures with dexamethasone markedly inhibited the stimulated production of prostaglandin E2 but had only a modest effect on basal production. Dexamethasone did not affect the activity of the enzyme protein kinase C, a putative regulator of eicosanoid synthesis. Our findings show that glucocorticoids have the potential to modulate central nervous system eicosanoid production particularly under conditions of stimulated production, such as inflammatory and demyelinating disorders. This mechanism may explain, at least in part, the therapeutic benefit of glucocorticoids in patients with multiple sclerosis.

Animals↗
PubMed1992

Mechanical injury increases eicosanoid production in cultured cardiomyocytes.

The release of three stable metabolites of the arachidonic acid cascade was determined in cultures of cardiac myocytes and of non-muscle cells. In both cell types, the main product was 6-keto-PGF1 alpha much less PGE2 was released, while TXB2 was only detected in muscle cells. Preincubation with arachidonic acid increased the release of all the PGs in both types of culture. Mechanical injury had a synergistic effect on the increased PG release in AA-preincubated cells. However, TXB2 was not detected in F-cells in any experimental conditions. These results suggest that PG production serves a functional role in heart preservation during injury.

6-Ketoprostaglandin F1 alpha↗
PubMed1992

Role of the central adrenergic system in the regulation of prostaglandin biosynthesis in rat brain.

The role of endogenous catecholamines in the regulation of brain prostaglandin (PG) synthesis was studied in the rat. Male rats were injected in the brain lateral ventricle or in the ventral noradrenergic bundle with either the catecholaminergic neurotoxin 6-hydroxydopamine or vehicle. Other groups of rats were injected intraperitoneally with the tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine, or with the inhibitor of dopamine-beta-hydroxylase, FLA-63. All these drugs produced a significant depletion of norepinephrine (NE) content in the cortex and hypothalamus. The rats that had lower levels of NE exhibited reduced capacity to synthesize PGE2 but not thromboxane B2 and 6-keto-PGE1 alpha in the cortex and hypothalamus. However, induced production of PG, stimulated by the bacterial endotoxin lipopolysaccharide (LPS), remained unchanged, namely, a similar (2- to 2.5-fold) increase of PG synthesis was noted in control and in NE-depleted rats. We suggest that the regulation of PG synthesis under basal condition requires intact adrenergic input, whereas LPS-induced production of PG is independent of the adrenergic innervation.

6-Ketoprostaglandin F1 alpha↗
PubMed1992

Methylprednisolone does not decrease eicosanoid concentrations or edema in brain tissue or improve neurologic outcome after head trauma in rats.

Methylprednisolone was recently reported to significantly improve motor and sensory function after acute spinal cord injury in patients. Our study was designed to determine whether methylprednisolone exerts a beneficial effect after head injury. Diethyl ether-anesthetized rats were assigned to receive surgery with no cranial impact and no methylprednisolone (group A, n = 13); surgery with no cranial impact and intraperitoneal methylprednisolone (greater than or equal to 60 mg/kg) (group B, n = 8); surgery with cranial impact and no methylprednisolone (group C, n = 8, and group E, n = 8); or surgery with cranial impact and methylprednisolone (greater than or equal to 60 mg/kg) (group D, n = 15, and group F, n = 13). Neurologic severity score was determined at 1, 2, 4, and 24 h (when appropriate) after injury, and brain tissue eicosanoid levels and cerebral edema were determined when the animals were killed (4 h after injury in groups C and D and 24 h after injury in groups E and F). Treatment with methylprednisolone did not improve neurologic severity score or edema formation and did not alter brain tissue levels of prostaglandin E2, thromboxane B2, or 6-keto-prostaglandin F1 alpha at any time period. The authors conclude that methylprednisolone does not exert a beneficial effect on brain tissue edema or functional activity after cranial impact in rats.

Animals↗
PubMed1990

Lethal hypoglycemia and hypothermia induced by administration of low doses of tumor necrosis factor to adrenalectomized rats.

An increased sensitivity of adrenalectomized (Adex) rats to intravenous (IV) injection of recombinant human tumor necrosis factor (rHuTNF) was manifested by a marked increase in the rate of mortality. The rats that died exhibited severe hypoglycemia and hypothermia. Administration of 2.5 or 10 micrograms/100 g body weight (3% or 12%) of the lethal dose in sham-operated rats (90 micrograms/100 g body weight) rHuTNF caused a mortality rate of 50% or 100%, respectively, within 4 hours of its injection. Pre-administration of dexamethasone or intermittent glucose infusion protected the animals from the lethal effect of rHuTNF. Indomethacin did not change the mortality rate in rHuTNF-treated Adex rats, but prevented it in sham-operated rats. The rats that died exhibited a marked decrease in body temperature, but only Adex rats developed hypoglycemia after low doses of TNF. Pretreatment with dexamethasone prevented the hypothermia in both Adex and sham-operated rats, while indomethacin was effective only in sham-operated rats and did not prevent the hypothermia or the hypoglycemia in Adex rats. In the surviving rHuTNF-treated Adex rats, a rapid increase in body temperature occurred, blood glucose decreased to 30 mg/dL, serum insulin concentration decreased to 6 microU/mL, liver glycogen content was reduced by 98%, and a significant reduction in liver phosphoeonolpyruvate carboxykinase (PEPCK) and liver microsomal glucose-6-phosphatase activities was observed. Repeated administration of glucose IV to rHuTNF-treated Adex rats caused an increase in blood glucose and insulin concentrations, and some repletion in liver glycogen content. Injection of rHuTNF, 2.5 to 10 micrograms/100 g body weight, to sham-operated rats caused a significant but slower increase in body temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Medulla↗
PubMed1990

Protective effect of MK801 in experimental brain injury.

The effect of a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, MK801, was studied in a model of closed head injury in rats. Head trauma (HT) was induced over the left cerebral hemisphere by a calibrated weight-drop device. One or 3 h later, MK801 in saline was given i.p. in a single bolus of either 1, 3, or 10 mg/kg. The rats were killed at 4, 24, or 48 h after HT. Cortical tissue samples were taken from the injured zone and from the corresponding region of the contralateral hemisphere and analyzed for specific gravity (SG) by linear gradient columns. The neurological status of the traumatized rats was evaluated by a neurological severity score (NSS) 1 h after trauma and just before death. Pathological evaluation, based on size and severity of the lesion, was performed 24 and 48 h after HT on control and MK801-treated rats. A dose of 3 mg/kg MK801 given 1 h after trauma effectively prevented the reduction in tissue SG only at 24 h. The NSS could not be evaluated at 24 h after trauma because of the sedating effect of the drug. At 48 h posttrauma, however, the drug significantly improved the neurological state of the rats. No significant difference was found in the pathological score between treated and untreated rats. The results demonstrate neuroprotective properties of MK801, as expressed in two different variables--reduced edema formation and improved neurological recovery after HT. These findings support existing evidence that pharmacological intervention with NMDA receptor antagonist after head injury may be of clinical value in the management of head-injured patients.

Animals↗
PubMed1990

Experimental neoplastic spinal cord compression: effect of ketamine and MK-801 on edema and prostaglandins.

Excitotoxin-induced neural tissue damage is mediated through specific receptors. We studied the in vivo effect of two selective N-methyl-D-aspartate receptor antagonists on the compressed spinal cord segments of rats harboring a thoracolumbar epidural tumor. The effect of a single intramuscular treatment with either MK-801 (3 mg/kg) or ketamine (110 mg/kg) given at the onset of paraplegia was evaluated 30 hours later. In saline-treated control animals, significant increases in water content, prostaglandin E2, and 6-keto-prostaglandin F1 alpha were evident. Treatment with either agent resulted in a normal water content in the compressed segments but had no effect on prostaglandin synthesis. Evaluation of the effect of treatment on the course of the disease required dose reduction by 45% for ketamine and by 30% for MK-801, to avoid the excessive sedative effect. Treatment was started at the first appearance of neurological dysfunction (Grade 1) and continued to paraplegia (Grade 5). The mean time interval between Grades 1 and 5 was 2.1 +/- 0.3 days in saline-treated control animals, and it was not significantly altered by either ketamine or MK-801. Our study indicates that in the end stage of epidural compression, when ischemia is present, excitotoxins probably participate in the evolution of a cytotoxic edema. It is suggested that treatment initiated at the onset of paraplegia may still reduce the cytotoxic edema, but its potential clinical value requires further investigations.

Analysis of Variance↗
PubMed1979

A kinetic analysis of the uptake of cytosine-beta-D-arabinoside by rat-B77 cells. Differentiation between transport and phosphorylation.

We present here a differentiation by kinetic methods of the tandem processes of transport and metabolic during uptake of cytosine-beta-D-arabinoside by intact rat fibroblasts. Transport across the cell membrane occurs by a carrier-mediated mechanism displaying a Km of approximately 500 microM and a V of approximately pmol x min-1 x (10(6) cells)-1. The subsequent metabolic trapping (phosphorylation) has a Km of approximately 15 microM and V of approximately 0.25 pmol x min-1 x (10(6) cells)-1. In this system, transport is rate-limiting for the first phase of the uptake process whereas phosphorylation becomes rate-limiting when internal concentration of radioactive labeled substrate exceeds that in the extracellular medium. The duration of the first phase depends on the substrate concentration.

Animals↗
PubMed1979

S-(N-dansylaminoethyl)-6-mercaptoguanosine as a fluorescent probe for the uridine transport system in human erythrocytes.

A fluorescent derivative of 6-mercaptoguanosine, S-(N-dansylaminoethyl)-6-mercaptoguanosine, was synthesized, and found to be a strong inhibitor of the uridine transport system of erythrocyte (Ki approximately 0.3 microM). The emission spectrum of this compound has peaks at 400 and 550 nm. The emission at 550, but not that a 400 nm, in environment-sensitive. A method was devised for preparing a suspension of erythrocyte-membrane fragments with sufficiently low light scattering so that a detailed study could be made of the fluorescence of the probe when bound to membranes. Direct binding measurements showed the existence of a tight binding site, with a dissociation constant of the same order of magnitude as the inhibition constant. Binding of probe and substrate are not mutually exclusive, but the fluorescence and affinity of the bound probe are sensitive to the presence of uridine. The emission spectrum suggests that the bound probe penetrates into the bilayer region of the membrane.

Binding Sites↗
PubMed1978

Nucleoside transport in mammalian cell membranes. IV. Organomercurials and organomercurial-mercaptonucleoside complexes as probes for nucleoside transport systems in hamster cells.

Organomercurials form stable stoichiometric complexes with thiolated nucleosides. The complexes inhibited uptake of ribonucleosides and cytosine arabinoside (CAR) in various types of normal and transformed cells. The inhibition was competitive and reversible (Ki = 3--6 micrometer). The interaction between complexes and transport system displayed a 1:1 stoichiometry. Chemical factors which contributed to the inhibitory power were evaluated with a series of S-alkylated derivatives and S--Hg--R complexes of mercaptonucleosides. The inhibitory potency was not determined exclusively by the hydrophobic nature of either the S-alkylated or the S--Hg--R moieties. Chemical modification of cells with penetrating and nonpenetrating organomercurials lead to stimulation of nucleoside uptake and to an increase in its susceptibility to inhibition by S--Hg--R complexes or S-aklylated derivatives of mercaptopurine ribosides. The kinetic and chemical data obtained with nucleoside analogs and with chemical modifiers suggested complex features of nucleoside transport systems. Four distinct classes of sites were implied: (i) a substrate binding site susceptible directly to competitive inhibition by organomercurial-mercaptonucleoside complexes, (ii) an additional site susceptible either to S-arylalkylated or S-mercuriated derivatives of 6-mercaptopurine ribosides, (iii) SH-containing modifier sites which stimulate uridine uptake upon binding of organomercurials, and (iv) SH-containing modifier sites which inhibit the function upon binding of organomercurials. From the observation that only SH sites related to stimulation were susceptible to modification by macromolecular-SH modifier probes, some conclusions can be drawn regarding the disposition of the various sites in the cell membrane in general and among membrane components in particular.

Binding, Competitive↗
PubMedDate not supplied

Superoxide dismutase activity is not affected by closed head injury in rats.

Superoxide anion radicals are generated in association with prostaglandin production, and are implied in the mediation of secondary brain damage following cerebral ischemia or injury. In a model of closed head injury in rats we have demonstrated the activation of phospholipase A2 (PLA2) and the increased production of eicosanoids in the post-trauma period. In the present study we investigated the role of superoxide dismutase (SOD) in this model. Head trauma was induced over the left cerebral hemisphere of ether anesthetized rats by a calibrated weight drop device. Cortical tissue samples were taken 15 min, 4 and 24 h later. SOD activity was assayed by its ability to inhibit the xanthine oxidase-cytochrome c reduction. There was no significant change in SOD activity in any of the regions studied - the site of injury, and contralateral region as well as the remote frontal lobes of both hemispheres. Although intense PLA2 activity and production of eicosanoids was previously found in some of these regions, activity of SOD was unaffected. These results do not support an important role for endogenous SOD up to 24 h after head injury.

Animals↗
PubMedDate not supplied

The mixed lipoxygenase/cyclooxygenase inhibitor SK&F 105809 reduces cerebral edema after closed head injury in rat.

Closed head injury in rats induces edema formation, which is indicated by a decrease in cerebral specific gravity and an increase in water content. We previously described the activation of the eicosanoid metabolic cascade, namely, activation of PLA2 and accumulation of products of both 5-lipoxygenase (5-LO) and cyclo-oxygenase (CO) in the same model of head injury. The present study was designed to determine the effect of a novel drug, SK&F 105809, a dual inhibitor of 5-LO and CO on cerebral edema formation after head injury in rats. Rats, under ether anesthesia, were subjected to sham operation or trauma induced by weight-drop device impacting over the left calvarium. One group of traumatized rats received 0.9% saline and served as control and two other groups were treated with SK&F 105809, 20 or 30 mg/kg, i.p. immediately after the impact. In one group treatment was repeated additionally 2.5 h post-trauma. Four hours after trauma, rats were sacrificed and brain edema was evaluated. SK&F 105809 treated rats which received 30 mg/kg had significantly less brain edema, as measured by both gravimetry and water content, at 4 h after trauma. The lower dose, 20 mg/kg, had no effect. Our results suggest that treatment with a mixed 5-LO/CO inhibitor shortly after head injury will result in less brain edema and ultimately improved functional outcome.

Animals↗