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Biomedical subjects

J A Clemens

Publications and source records attributed to J A Clemens.

At least 37 records · Page 2Linked to original sources
PubMed1996

Cytosolic phospholipase A2 (cPLA2) and lipid mediator release in the brain.

The Ca(2+)-sensitive 85 kDa cytosolic PLA2 (cPLA2) is a receptor-regulated enzyme that may initiate the cascade of events leading to the production of free fatty acids and lysophospholipids for subsequent conversion to eicosanoids and PAF. At least two early events are necessary for full activation of cPLA2: (1) increased concentration of cytosolic free Ca2+ promoting association of cPLA2 with its membrane phospholipid substrate and (2) phosphorylation by stimulated proline-directed kinases converting cPLA2 into an enzyme of enhanced catalytic efficiency. Moreover, pro-inflammatory cytokines, such as IL-1 and TNF may induce de novo synthesis of cPLA2 thus further potentiating the mobilization of arachidonic acid and subsequent production of eicosanoids and PAF. Increased levels of fatty acids and PLA2-derived products, including eicosanoids and PAF are amongst the hallmarks of cerebral ischemia and reperfusion, and thought to mediate pathophysiological alterations and cellular processes which may lead to cell injury and death. There is substantial evidence to indicate that cPLA2 is present in the brain and appears most abundant in astrocytes. Therefore, cPLA2 may be an important component in the cascade of events leading to acute and delayed destructive cellular processes in the brain and accordingly represents an attractive target for the development of novel therapies to prevent brain damage triggered by ischemic and inflammatory insults.

Animals↗
PubMed1996

Induction of sulfated glycoprotein-2 (clusterin) and glial fibrillary acidic protein (GFAP) RNA expression following transient global ischemia is differentially attenuated by LY231617.

Sulfated glycoprotein-2 (SGP-2) is a secreted glycoprotein that along with GFAP has emerged as a prominent molecular marker of neurodegeneration. In the present study, we have evaluated further the relationship between SGP-2, GFAP and neurodegeneration, by examining the effects of LY231617, a potent antioxidant, on expression of SGP-2 and GFAP following four vessel occlusion (4VO). GFAP and SGP-2 RNA levels increased several fold in hippocampus and caudate nucleus in response to 30 min of 4VO. LY231617 treatment markedly attenuated the induction of GFAP RNA in both hippocampus and caudate nucleus, consistent with the significant neuroprotection observed histologically. In contrast, LY231617 treatment blunted SGP-2 RNA expression only in the hippocampus; SGP-2 RNA expression in caudate nucleus was similar to vehicle-treated 4VO, despite the marked attenuation of neuronal damage in both areas by LY231617. These data suggest region-specific differential regulation of SGP-2 and GFAP RNA induction.

Animals↗
PubMed1996

The efficacy of retrograde infusion with LY231617 in a rat middle cerebral artery occlusion model.

BACKGROUND AND PURPOSE: We examined the efficacy of the antioxidant LY231617 administered five hours following middle cerebral artery (MCA) occlusion in rats. METHODS: The treatment was contrived for a two hour interval. Group A (n = 16) was left untreated. Group B (n = 16) received an intravenous infusion of LY231617. Group C (n = 16) received saline (86 microliters/min) by retrograde infusion of the cerebral vein (RICV). Group D (n = 22) was administered LY231617 (10mg/kg/2 hr) in saline (86 microliters/min) by RICV. Local cerebral blood flow with [14C]-iodoantipyrine and blood-brain transfer constant with 14C-alpha-amino-isobutyric acid were examined. Early ischemic damage was histologically examined with cresyl violet and Luxol fast blue and with triphenyl-tetrazolium chloride. RESULTS: The results revealed a marked increase in local cerebral blood flow (over 600%, p < 0.01) after RICV with LY231617, with a significant improvement of BBB permeability in rats from group D. Ischemic brain damage measured with Luxol fast blue and triphenyl-tetrazolium chloride methods showed a significant improvement (50-91%) of ischemic damage in group D, as compared to groups B and C. CONCLUSION: Retrograde infusion of the cerebral vein with LY231617 resulted in a significant amelioration at seven hours post MCA occlusion.

Animals↗
PubMed1996

Reactive glia express cytosolic phospholipase A2 after transient global forebrain ischemia in the rat.

BACKGROUND AND PURPOSE: Phospholipid breakdown has been reported to be an early event in the brain after global cerebral ischemia. Our earlier observations showing the localization of cytosolic phospholipase A2 (cPLA2) to astrocytes in aged human brains and the intense glial activation observed after global forebrain ischemia prompted us to investigate the cellular localization of cPLA2 in the rat brain subjected to global ischemia. METHODS: Immunohistochemistry was performed in sections through the dorsal hippocampus in rats subjected to 30 minutes of four- vessel occlusion. PLA2 was localized with the use of a highly selective antiserum. Double immunofluorescent localization was performed to colocalize cPLA2 with various glial cell types. cPLA2 levels were also measured by enzymatic assay and Western blot analysis. RESULTS: A marked induction of cPLA2 was observed in activated microglia and astrocytes in the CA1 hippocampal region at 72 hours after ischemia. Only a subset of astrocytes and microglia were immunoreactive for cPLA2. Twenty-four hours after ischemia, numerous cPLA2 immunoreactive astrocytes were observed. Western blot analysis of hippocampal homogenates at 72 hours after ischemia showed induction of a 100-kD band that comigrated with purified human cPLA2, and a threefold induction in cPLA2 activity was demonstrated by enzymatic assay. CONCLUSIONS: These results indicate that both reactive astrocytes and microglia contain elevated levels of cPLA2. Induction of cPLA2 was confined to areas of neurodegeneration and likely precedes its onset. The results suggest that reactive glia may play a role in the pathophysiology of delayed neuronal death after transient global forebrain ischemia.

Animals↗
PubMed1995

Ischemia increases tissue and decreases extracellular levels of acid dopamine metabolites in the rat striatum: further evidence for active transport of metabolites.

During 30 minutes of global forebrain ischemia in rats, striatal intracellular levels of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) increase at the same time extracellular levels, measured by microdialysis, decrease. If DOPAC and HVA were free to diffuse out of cells, these changes in opposite directions should not occur. These data support the theory that a membrane potential-dependent active transport system is required for DOPAC and HVA to leave striatal cells. During ischemia and subsequent to ATP depletion, neurons and glia depolarize and active transport systems fail. DOPAC and HVA, which are still being produced inside neurons and possibly glia, can not be transported out of these cells and accumulate intracellularly.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1995

Increase in insulin-like growth factor II receptor within ischemic neurons following focal cerebral infarction.

The mechanisms underlying the response of the brain to ischemia are not fully understood. Biochemical and morphological changes following neocortical infarction can be investigated in rats using a model of focal cerebral ischemia induced by unilateral occlusion of the middle cerebral artery (MCA). Evaluation of ischemic damage often employs conventional histologic stains. Immunocytochemistry can be used as a valuable tool in this model to define changes in specific proteins of interest. In this study, an antiserum raised against insulin-like growth factor II (IGF-II) receptor was used to evaluate changes of IGF-II receptor immunoreactivity in the cerebral cortex of rats 4 and 7 days following permanent MCA occlusion. IGF-II receptor immunoreactivity was found to be associated with neocortical pyramidal neurons within the core of the ischemic infarct itself. The staining intensity was markedly elevated above that observed in nonischemic neurons. Immunopositive neurons exhibited a punctate staining pattern. These neurons appeared to correspond to argentophilic neurons, as defined by modified Bielschowsky silver staining. Evaluation of other neuronal markers revealed the absence of immunoreactivity for neuron-specific enolase and for tyrosine hydroxylase within the ischemic area. These observations show an increase in a specific growth factor receptor within neurons in the ischemic core of a focal infarct several days following permanent focal infarction, a time when neurons are presumed to be dead. The significance and the potential role of IGF-II receptor in lesion-induced plasticity are discussed.

Animals↗
PubMed1995

Peripheral benzodiazepine receptors are colocalized with activated microglia following transient global forebrain ischemia in the rat.

In mammalian brain the expression of peripheral benzodiazepine receptors (PBRs) can be markedly induced following different types of neuronal injury. PBRs are believed to be expressed on non-neuronal cells in the brain, yet the specific cell type that expresses these receptors following CNS insult has not been defined. In the present study, we investigated the effects of transient global forebrain ischemia on PBRs by autoradiographic localization of 3H-PK11195 binding. The distribution of PBRs was compared to glial fibrillary acidic protein (GFAP) as a marker for astrocytes and OX42 as a marker for microglia. Five to 6 d following four-vessel occlusion (4-VO), an increase in PBRs was seen in the CA1 region of all 15 brains examined. In brains from rats subjected to 4-VO, microglia were selectively activated in stratum pyramidale of the CA1 layer. In contrast, astrocytes appeared to be activated in multiple hippocampal cell layers including stratum radiatum and stratum oriens. Activated astrocytes were also found in regions that did not exhibit increased 3H-PK11195 binding. In some brains, selected regions of secondary lesion, specifically necrotic thalamic nuclei and the isocortex were found to be strongly immunoreactive for OX42 but lacked GFAP immunoreactive cells. In adjacent sections, these same regions displayed high densities of 3H-PK1195 binding. These observations lend further support to the application of 3H-PK11195 binding as a marker of neuronal injury in the brain. Furthermore, the data strongly suggest that activated microglia rather than astrocytes express PBRs following ischemic insults.

Animals↗
PubMed1994

Preservation of a functionally intact neuronal network after global ischemia.

Although conventional histological techniques demonstrated preservation by drug treatment of neuronal perikarya in the hippocampal CA1 region in animals subjected to short periods of transient ischemia, uncertainty exists regarding whether the anatomical connections with these neurons are intact and functional. The hippocampal theta rhythm is dependent upon intact connections to the CA1 pyramidal neurons and is a useful predictor of functional hippocampal integrity. Hippocampal theta was quantitated by power spectral analysis in rats subjected to 30 min of 4-vessel occlusion (4-VO) and treatment with the neuroprotective antioxidant, LY231617. The 4-VO destroyed CA1 neurons and reduced the amount of theta, however, LY231617 protected CA1 neurons histologically and totally preserved the hippocampal theta rhythm. We conclude that histological preservation is indicative of functional integrity.

Animals↗
PubMed1994

Calcium-sensitive cytosolic phospholipase A2 (cPLA2) is expressed in human brain astrocytes.

Calcium-sensitive cytosolic phospholipase A2 (cPLA2) is responsible for receptor-mediated liberation of arachidonic acid, and thus plays an important role in the initiation of the inflammatory lipid-mediator cascade generating eicosanoids and platelet-activating factor. In this study we have investigated the cellular distribution of cPLA2 in brain using a monoclonal antibody raised against cPLA2 to immunostain tissue sections of human cerebral cortex. We have localized cPLA2 in astrocytes of the gray matter. Colocalization with glial fibrillary acidic protein (GFAP) confirmed that cPLA2 is associated predominantly with protoplasmic astrocytes. Astrocytes of the white matter, on the other hand, were not immunoreactive. In experiments using different human astrocytoma cell lines we found that cPLA2 can be immunochemically localized in UC-11 MG cells, but cannot be detected in U-373 MG cells. This finding is consistent with the observation that cPLA2 mRNA as well as cPLA2 enzymatic activity can be readily measured in UC-11 MG astrocytoma cells, yet cannot be detected in U-373 MG cells. Our data suggest that the astrocyte is a primary source of cPLA2 in the brain and provide further evidence for the importance of this cell type in inflammatory processes in the brain.

Adult↗
PubMed1994

LY226936 administered orally and centrally to obese Zucker rats suppresses food intake and body weight gain.

LY226936, methylcarbamothoic acid-S-(4,5-dihydro-2-thiazolyl) ester, is a new compound that, when administered to obese Zucker rats, caused reduced food intake. LY226936 reduced the food consumption after a single oral dose of 50 and 100 mg/kg. On chronic oral administration to meal-fed obese (5 to 35 mg/kg. once daily) and to fed obese and lean (15 mg/kg. twice daily) Zucker rats, LY226936 reduced food intake and body weight gain for periods ranging from 40 to 48 days. The effect on both parameters was statistically significant. There is no evidence in our studies that tolerance to the actions of LY226936 developed. LY226936 decreased the consumption of both high carbohydrate and high fat diets. Food consumption of meal-fed obese Zucker rats was reduced significantly each time a single dose of 10 ugm LY226936 per rat was infused intracerebroventricularly. None of the receptors studied (mu and kappa opioid, CCK, serotonin, neuropeptide Y, galinin, N-methyl-D-aspartic acid) appeared to bind LY226936 and therefore, appear not to be involved in the depression of food intake by the obese Zucker rat.

Administration, Oral↗
PubMed1993

Decrease in amyloid precursor protein precedes hippocampal degeneration in rat brain following transient global ischemia.

We have studied amyloid precursor protein (APP) expression in rat brain following transient global ischemia. Ischemic damage 24 h after 30 min of four-vessel occlusion (4VO) was limited to the caudate nucleus; hippocampal pyramidal neurons appeared histologically normal by light microscopy. Consistent with ongoing neurodegeneration in the caudate nucleus, microtubule-associated protein-2 (MAP-2) levels assessed by immunoblots were significantly reduced in homogenates of caudate nucleus after 4VO. MAP-2 levels In the hippocampus were comparable to control values. In contrast, full length APP levels in both the caudate nucleus and hippocampal homogenates were significantly decreased following 4VO despite normal hippocampal morphology at 24 h. These findings suggest that decrements in full length APP precede overt neuronal damage and may play a role in the subsequent delayed neurodegeneration in the hippocampus.

Amyloid beta-Protein Precursor↗
PubMed1993

Synthesis and dopamine antagonist activity of 2-thioether derivatives of the ergoline ring system.

A series of 2-thioether derivatives of a number of clavine alkaloid (ergoline) ring systems have been synthesized and tested for dopamine antagonist activity. Of the compounds tested 2-(methylthio)-agroclavine (8,9-didehydro-6,8-dimethyl-2-(methylthio)ergoline) (6) was the most potent and had a profile of activity in animal models indicative of potential antipsychotic activity. The synthesis and biological activity of a number of metabolites of 6, including the 13-hydroxy derivative, are also reported.

Animals↗
PubMed1993

Endocrine and antiprostatic effects of raloxifene (LY156758) in the male rat.

The benzothiophene anti-estrogen, raloxifene [LY156758; (6-hydroxy-2-(4-hydroxyphenyl) benzo(b)thien-3-yl)(4-(2-1-piperidinyl)ethoxy)phenyl methanone hydrochloride] has selective estrogen pharmacological antagonist activity in female rats. The present studies were done in the male rat to assess activity of raloxifene related to inhibition of prostatic growth and effects on the hypothalamic-pituitary-gonadal axis. Raloxifene did not compete for binding of the androgen, [3H]-methyltrienolone (R1881) in cytosolic extracts of ventral prostate. Similarly, the compound did not inhibit prostatic 5 alpha-reductase or testicular 17 alpha-hydroxy/C17,20-lyase activities. Raloxifene had no effect on the ventral prostatic uptake of [3H]-R1881 in vivo. Administration of estradiol to castrated male rats stimulated fourfold increases of in vitro ventral prostatic binding of [3H]-R1881. Raloxifene was devoid of agonist activity in castrated animals, because the compound had no stimulatory effect on prostatic androgen receptor binding activity. When raloxifene was coadministered with estradiol, the compound markedly antagonized the estrogen-induced increase of prostatic [3H]-R1881 binding, confirming its antiestrogenic properties in male rats. Serum prolactin was also elevated significantly (P < 0.05) with a single injection of raloxifene (20.0 mg/kg). In these same animals, serum FSH was significantly (P < 0.05) decreased by one dose (10.0 mg/kg) of the compound. Luteinizing hormone levels in castrated male rats were unaffected by raloxifene administration. Raloxifene treatment of castrated males significantly (P < 0.05) antagonized the stimulatory response of the ventral prostate (VP) to exogenous androgens in a dose-dependent manner. Raloxifene treatment of intact male rats for 14 and 28 days produced significant (P < 0.05) dose-dependent regression of the VP and seminal vesicles (SV). The VP regressive responses to raloxifene were associated with a decline in serum testosterone levels. Histological analysis of the VPs in raloxifene-treated rats was consistent with an androgen-deprived state. These findings support the contention that raloxifene is a pure estrogen antagonist and a physiological antagonist of androgen action in male rats. These pharmacological properties provide support for further structure-activity and mechanistic investigations with benzothiophenes in the medical management of prostatic neoplasia.

Aldehyde-Lyases↗
PubMed1993

The antioxidant LY231617 reduces global ischemic neuronal injury in rats.

BACKGROUND AND PURPOSE: In the rat four-vessel occlusion model with 30 minutes of ischemia most agents have failed to be of benefit when given after ischemia. Because postischemia administration is more clinically relevant, we evaluated the antioxidant LY231617 (2,6-bis(1,1-dimethylethyl)-4-[[(1-ethyl)amino]methyl]phenol hydrochloride]) when administered after 30 minutes of four-vessel occlusion. METHODS: Male Wistar rats were subjected to 30 minutes of four-vessel occlusion. LY231617 was either given orally 30 minutes before ischemia or intravenously beginning at 30 minutes after the onset of ischemia. Hippocampal CA1 layer and striatal damage were rated on a scale of 0-3 (0, no damage; 3, > 90% cell loss). We also evaluated the ability of LY231617 to prevent iron-dependent lipid peroxidation and to prevent hydrogen peroxide-induced neuronal death of hippocampal neurons in primary culture by exposing cultures to a 50-microM concentration of hydrogen peroxide for 15 minutes in the presence of LY231617. RESULTS: Oral administration of LY231617 reduced both striatal and hippocampal CA1 damage by > 75% (p < 0.0001). In two separate experiments in which LY231617 was given intravenously beginning 30 minutes after occlusion, hippocampal and striatal damage were reduced by approximately 50% (p < 0.03) in the first experiment and by approximately 41% (p < 0.02) in the second experiment. Addition of 5 microM of LY231617 to primary hippocampal neuronal cultures antagonized the lethal effect of hydrogen peroxide (p < 0.05). Iron-dependent lipid peroxidation was also inhibited in a dose-related fashion. CONCLUSIONS: The significant reduction of ischemia-induced or hydrogen peroxide-induced neuronal damage and inhibition of lipid peroxidation by LY231617 observed in this study suggest that reactive oxygen intermediates play an important role in the events leading to neuronal death after global ischemia/reperfusion.

Animals↗
PubMed1993

Progress in the medicinal chemistry of dopaminergic agents.

Ergot alkaloids and their derivatives have long been recognized for their potent pharmacologic activity. A number of ergot derivatives, including the dopamine agonists bromocriptine and pergolide, are currently in clinical use for the treatment of CNS and endocrine disorders. In an effort to develop more selective dopamine agonists, studies were directed to elucidate the dopaminergic pharmacophore of the ergoline nucleus. During the course of this work, it was found that the tricyclic system containing only the B-, C-, and D-rings of the ergoline skeleton (2, X = CH) possessed D-2 dopamine agonist activity. As a result of this discovery, interest was stimulated in the preparation of other heteroareno[g]quinoline systems (3, "BCD partial ergolines") for investigation of their dopaminergic properties. Factors which we found to be particularly important in determining dopaminergic activity were: (1) the nature of the heteroaromatic B ring; (2) the orientation of that heteroaromatic ring; (3) the substituents on the heteroaromatic ring; and (4) the relative and absolute stereochemistry at the CD ring fusion. We report here the synthesis and pharmacologic activity of a series of BCD partial ergolines (3) and describe how the study of these new compounds allows for the delineation of structural features important in D2 dopamine receptor activation.

Animals↗
PubMed1993

Microinjection of synthetic amyloid beta-protein in monkey cerebral cortex fails to produce acute neurotoxicity.

The cerebral deposition of amyloid beta protein (A beta P) is an early pathogenetic event in Alzheimer's disease (AD). Recent studies suggest both neurotoxic and neurotrophic effects of A beta P in vitro. Because progressive A beta P deposition and surrounding neuritic dystrophy occur spontaneously in primates, we evaluated the in vivo effects of synthetic A beta P in monkey cortex. Experimental and control (reverse or substituted) peptides were stereotactically injected into multiple neocortical sites of adult rhesus monkeys in a vehicle of either artificial cerebrospinal fluid or acetonitrile. After 2 weeks, all injection sites were identified and characterized. A beta P antibodies specifically detected the injected A beta P1-40 peptide. Serial sections stained with silver and antineurofilament protein demonstrated comparable degrees of degenerating neurons, dystrophic neurites, and axonal spheroids associated with both experimental and control peptide injections. Alz 50 staining was sparse or absent in all sites. Similar results were obtained in an animal killed 3 months after injection. We conclude that specific cellular changes closely resembling the pathology of Alzheimer's disease were not detected in these acute experiments, and that control and experimental A beta P peptides produced indistinguishable effects.

Alzheimer Disease↗