Vargas HM

References (11)

Title : Pharmacological activity and safety profile of P10358, a novel, orally active acetylcholinesterase inhibitor for Alzheimer's disease - Smith_1997_J.Pharmacol.Exp.Ther_280_710
Author(s) : Smith CP , Bores GM , Petko W , Li M , Selk DE , Rush DK , Camacho F , Winslow JT , Fishkin R , Cunningham DM , Brooks KM , Roehr J , Hartman HB , Davis L , Vargas HM
Ref : Journal of Pharmacology & Experimental Therapeutics , 280 :710 , 1997
Abstract : 1-[(3-Fluoro-4-pyridinyl)amino]-3-methyl-1(H)-indol-5-yl methyl carbamate (P10358) is a potent, reversible acetylcholinesterase inhibitor that produces central cholinergic stimulation after oral and parental administration in rats and mice. P10358 is a 2.5 times more potent acetylcholinesterase inhibitor than THA in vitro (IC50 = 0.10 +/- 0.02 microM vs. IC50 = 0.25 +/- 0.03 microM). It also inhibits butyrylcholinesterase activity as potently as THA (IC50 = 0.08 +/- 0.05 microM vs. IC50 = 0.07 +/- 0.01 microM). Ex vivo, P10358 (0.2 - 20 mg/kg, p.o.) produced dose-dependent inhibition of brain acetylcholinesterase activity. At 10 and 20 mg/ kg, it produced profound and long-lasting hypothermia in mice. P10358 enhanced performance in rats in a step-down passive avoidance task (0.62 and 1.25 mg/kg) and in a social recognition paradigm (0.32, 0.64 and 1.25 mg/kg) in mice. It reversed scopolamine-induced deficits in the Morris Water maze in rats (1.25 and 2.5 mg/kg) and a higher dose elevated striatal homovanillic acid levels. These behavioral and biochemical effects are consistent with central cholinergic stimulation. Hemodynamic studies in the rat demonstrated a 16-fold separation between behaviorally active doses (1.25 mg/kg) and those that elevated arterial pressure (20 mg/kg). Lethality in rats occurred at an oral dose of 80 mg/kg, but not at lower doses. Chemically, P10358 is an N-aminoindole and may not have the hepatotoxic liability associated with aminoacridine structure of tacrine. P10358 had weak affinity (>10 microM) at a variety of aminergic and peptidergic receptors and uptake carriers. These properties suggest that P10358 may be a safe and promising symptomatic treatment for Alzheimer's disease.
ESTHER : Smith_1997_J.Pharmacol.Exp.Ther_280_710
PubMedSearch : Smith_1997_J.Pharmacol.Exp.Ther_280_710
PubMedID: 9023283

Title : Alpha 2-adrenoceptor antagonists potentiate acetylcholinesterase inhibitor effects on passive avoidance learning in the rat - Camacho_1996_Psychopharmacology_124_347
Author(s) : Camacho F , Smith CP , Vargas HM , Winslow JT
Ref : Psychopharmacology , 124 :347 , 1996
Abstract : The cholinergic hypothesis of Alzheimer's disease (AD) has strongly influenced research on learning and memory over the last decade. However, there has been limited success treating AD dementia with cholinomimetics. Furthermore, there are indications that other neurotransmitter systems affected by this disease may be involved in cognitive processes. Animal studies have suggested that norepinephrine and acetylcholine may interact in learning and memory. The current experiments investigate this interaction in a step-down passive avoidance paradigm after coadministration of acetylcholinesterase inhibitors and alpha 2-adrenoceptor antagonists. Administration of acetylcholinesterase inhibitors heptylphysostigmine (0.625-5.0 mg/kg, IP), tacrine (2.5-10.0 mg/kg, PO), velnacrine (0.312-2.5 mg/kg, SC), and galanthamine (0.312-2.5 mg/kg IP) each enhanced retention of a passive avoidance response at selected moderate doses administered 30-60 min prior to training. The alpha 2-adrenoceptor antagonists idazoxan (0.312-2.5 mg/kg, IP), yohimbine (0.078-0.312 mg/kg, IP) and P86 7480 (0.156-0.625 mg/kg, IP) alone failed to enhance learning in this paradigm. Coadministration of a subthreshold dose of heptylphysostigmine (0.625 mg/kg, IP) with doses of idazoxan, yohimbine or P86 7480 enhanced passive avoidance learning. This synergistic interaction may represent effects of antagonism of presynaptic alpha 2-adrenoceptor since coadministration of heptylphysostigmine and the selective postsynaptic alpha 2-adrenoceptor antagonist SKF 104856 did not result in enhanced learning. Taken together these data suggest noradrenergic activation through pre-synaptic alpha 2-adrenoceptor blockade may potentiate cholinergic activity in the formation of a long-term memory trace. These observations may have implications for the treatment of AD with cholinergic and adrenergic agents.
ESTHER : Camacho_1996_Psychopharmacology_124_347
PubMedSearch : Camacho_1996_Psychopharmacology_124_347
PubMedID: 8739550

Title : Pharmacological evaluation of novel Alzheimer's disease therapeutics: acetylcholinesterase inhibitors related to galanthamine - Bores_1996_J.Pharmacol.Exp.Ther_277_728
Author(s) : Bores GM , Huger FP , Petko W , Mutlib AE , Camacho F , Rush DK , Selk DE , Wolf V , Kosley RW, Jr. , Davis L , Vargas HM
Ref : Journal of Pharmacology & Experimental Therapeutics , 277 :728 , 1996
Abstract : Acetylcholinesterase (AChE) inhibitors from several chemical classes have been tested for the symptomatic treatment of Alzheimer's disease; however, the therapeutic success of these compounds has been limited. Recently, another AChE inhibitor, galanthamine hydrobromide (GAL), has shown increased clinical efficacy and safety. Using biochemical, behavioral and pharmacokinetic analyses, this report compares GAL with two of its analogs, 6-O-acetyl-6-O-demethylgalanthamine hydrochloride (P11012) and 6-O-demethyl-6-O[(adamantan-1-yl)-carbonyl]galanthamine hydrochloride (P11149), for their therapeutic potential. P11012 and P11149 were found to be potent, competitive and selective inhibitors of AChE, demonstrating central cholinergic activity, behavioral efficacy and safety. P11012 and P11149, though pharmacokinetic analyses, were shown to act as pro-drugs, yielding significant levels of 6-O-demethylgalanthamine. In vitro, 6-O-demethylgalanthamine was 10- to 20-fold more potent than GAL as an inhibitor of AChE, and it demonstrated greater selectivity for inhibition of AChE vs. butyrylcholinesterase. Like GAL, both P11012 and P11149 showed central cholinergic activity biochemically, by significantly inhibiting rat brain AChE; physiologically, by causing hypothermia; and behaviorally, by attenuating scopolamine-induced deficits in passive avoidance. In addition, GAL, P11012 and P11149 enhanced step-down passive avoidance, another measure of behavioral efficacy. By comparing efficacious doses with primary overt effects, P11012 and P11149 had better oral therapeutic indices than GAL. Oral pharmacokinetic analyses of GAL, P11012 and P11149 revealed differences. Although P11012 and P11149 exhibited similar area under the curve values, 191149 had slower, lower and more sustained concentration maximum levels. P11012 and GAL rapidly reached their concentration maximums, but GAL, in brain had the highest area under the curve and concentration maximum. Because of its composite profile, including duration of action, oral therapeutic index and pharmacokinetics, P11149 is considered the better therapeutic candidate for the treatment of Alzheimer's disease.
ESTHER : Bores_1996_J.Pharmacol.Exp.Ther_277_728
PubMedSearch : Bores_1996_J.Pharmacol.Exp.Ther_277_728
PubMedID: 8627552

Title : Elevation of cerebrospinal fluid choline levels by nicotinamide involves the enzymatic formation of N1-methylnicotinamide in brain tissue - Vargas_1996_Life.Sci_58(22)_1995
Author(s) : Vargas HM , Jenden DJ
Ref : Life Sciences , 58 :1995 , 1996
Abstract : Nicotinamide administration can elevate plasma and brain choline levels and produce a marginal increase in striatal acetylcholine levels in the rat. We now report that subcutaneous nicotinamide produces a substantial and long-lasting rise in cisternal cerebrospinal fluid (CSF) levels of choline in free-moving rats, possibly through the enzymatic formation of N1-methylnicotinamide (NMN) in brain. CSF choline levels peaked 2 hours after nicotinamide administration and were accompanied by increases in striatal, cortical, hippocampal and plasma choline levels. The enzymatic formation of [3H]NMN in rat brain was evaluated by incubating aliquots of rat brain cytosol with unlabelled nicotinamide and the methyl donor [3H]S-adenosylmethionine. High performance liquid chromatography and radiochemical detection demonstrated that [3H]NMN was specifically formed by a brain cytosolic enzyme. The production of [3H]NMN was dependent on exogenous nicotinamide and could be prevented by denaturing the cytosol. The metabolism of nicotinamide to NMN in rat brain may explain the rise in CSF choline levels since NMN, a quaternary amine, can inhibit choline transport at the choroid villus and reduce choline clearance.
ESTHER : Vargas_1996_Life.Sci_58(22)_1995
PubMedSearch : Vargas_1996_Life.Sci_58(22)_1995
PubMedID: 8637429

Title : Effect of hemicholinium-3 on the hypothalamic concentration of a cytochemically detectable glucose-6-phosphate dehydrogenase-stimulating substance - Vargas_1994_J.Cardiovasc.Pharmacol_24_773
Author(s) : Vargas HM , Brezenoff HE , Morris HR , Panico M , Etienne A , Challand GS , Holland SM , Alaghband Zadeh J , de Wardener HE
Ref : J Cardiovasc Pharmacol , 24 :773 , 1994
Abstract : Hypothalamus and plasma of salt-loaded rats, spontaneously hypertensive rats (SHR), and hypertensive reduced renal mass rats (RRM), and the plasma of patients with essential hypertension and of Milan hypertensive rats contain an increased concentration of a cytochemically detectable glucose-6-phosphate dehydrogenase (G6PD)-stimulating substance that has properties similar to that of a possible choline derivative di-methyl methylene immonium ion. Intracerebroventricular (i.c.v.) administration of hemicholinium-3 (HC-3) selectively blocks high-affinity neuronal choline uptake, inhibits brain acetylcholine (ACh) synthesis, and decreases arterial pressure in SHR through an inhibiting effect on hypothalamic cholinergic function. The experiments were performed to study the effect of centrally administered HC-3 on the content of the cytochemically detectable cholinelike substance in hypothalamus and plasma of SHR. HC-3 or saline was infused into the lateral cerebral ventricle for 6 days with a minipump in 14 SHR. On day 7, the hypothalamic and plasma concentration of the cytochemically detectable substance was significantly reduced in rats that received HC-3. The hypothalamic concentration was 225 +/- 95.6 x 10(8) G6PD U per hypothalamus (range 38.2-775) in SHR that received saline and 1.037 +/- 0.45 x 10(8) G6PD U (range 0.112-3.61) (p < 0.05) in SHR that received HC-3. The respective plasma concentrations were 284.9 +/- 26 U/ml (range 192-374) and 72.7 +/- 14.7 U/ml (range 24-119) (p < 0.05). The findings are consistent with the physicochemical evidence, which suggests that the cytochemically detectable substance is a choline derivative.
ESTHER : Vargas_1994_J.Cardiovasc.Pharmacol_24_773
PubMedSearch : Vargas_1994_J.Cardiovasc.Pharmacol_24_773
PubMedID: 7532755

Title : Phenyl-substituted analogues of oxotremorine as muscarinic antagonists - Nilsson_1992_J.Med.Chem_35_285
Author(s) : Nilsson BM , Vargas HM , Ringdahl B , Hacksell U
Ref : Journal of Medicinal Chemistry , 35 :285 , 1992
Abstract : A series of phenyl-substituted analogues of the muscarinic agent oxotremorine (1) have been prepared. The new compounds (3b-11b and 9c) were assayed for antimuscarinic activity on the isolated guinea pig ileum and in intact mice. They were also evaluated for ability to inhibit the binding of the muscarinic antagonist (-)-[3H]-N-methylscopolamine to homogenates of the rat cerebral cortex. The phenyl-substituted derivatives were devoid of intrinsic muscarinic activity. Instead, they behaved as competitive muscarinic antagonists in these assays with similar or lower affinity for muscarinic receptors than the corresponding methyl-substituted analogues. The succinimide (8b) and the pyrrolidone (3b) derivatives of 1 substituted with a phenyl group at position 1 of the butynyl chain showed the highest antimuscarinic potency with dissociation constants (KD) of 0.10 and 0.20 microM, respectively, in the ileum assay. The phenyl-substituted analogues showed an approximately 10-fold lower in vivo antimuscarinic potency than their corresponding methyl-substituted positional isomers. A correlation was observed between in vitro and in vivo potency within subsets consisting of methyl- and phenyl-substituted derivatives.
ESTHER : Nilsson_1992_J.Med.Chem_35_285
PubMedSearch : Nilsson_1992_J.Med.Chem_35_285
PubMedID: 1732545

Title : Centrally active antimuscarinic analogs of oxotremorine selectively block physostigmine-induced hypertension, but not peripheral muscarinic vasodepression - Vargas_1990_J.Pharmacol.Exp.Ther_253_165
Author(s) : Vargas HM , Ringdahl B
Ref : Journal of Pharmacology & Experimental Therapeutics , 253 :165 , 1990
Abstract : Some tertiary antimuscarinic amines related to oxotremorine were compared with atropine and scopolamine for their ability to block physostigmine-induced hypertension and acetylcholine-induced hypotension in rats. These cardiovascular responses are mediated via muscarinic receptors in the brainstem and on the vasculature, respectively. In urethane-anesthetized rats, physostigmine (77 nmol/kg i.v.) increased mean arterial pressure 40 +/- 5 mm Hg. One hour later, each rat received a single dose of antimuscarinic, then a second bolus of physostigmine 10 min later. Linear regression analysis of antagonist dose-percent inhibition curves showed that all the agents inhibited physostigmine's pressor effect, thus indicating an ability to antagonize brain muscarinic receptors. BM-5 and BoK-1 were estimated to be equipotent with atropine, all having 50% inhibitory doses (ID50) in the 1.5 to 1.8 mumol/kg range. BR-370 and DKJ-21 were 3- and 30-fold less potent, respectively, than atropine in this assay, while scopolamine was the most potent (ID50: 0.039 mumol/kg). In contrast with atropine and scopolamine, the oxotremorine analogs possessed selective central antimuscarinic effects and were completely unable to antagonize the peripheral depressor response. Like atropine, only BM-5 showed significant tachycardiac effects, which suggested that this agent possessed affinity for myocardial muscarinic receptors. These findings support the concept that congeners of oxotremorine behave as centrally selective antimuscarinics at doses which have low peripheral antimuscarinic activity in vivo. This unique pharmacological profile makes them novel probes to study central cholinergic muscarinic mechanisms in cardiovascular regulation.
ESTHER : Vargas_1990_J.Pharmacol.Exp.Ther_253_165
PubMedSearch : Vargas_1990_J.Pharmacol.Exp.Ther_253_165
PubMedID: 2329503

Title : Resolved pyrrolidine, piperidine, and perhydroazepine analogues of the muscarinic agent N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)acetamide - Lundkvist_1990_J.Med.Chem_33_3182
Author(s) : Lundkvist JR , Vargas HM , Caldirola P , Ringdahl B , Hacksell U
Ref : Journal of Medicinal Chemistry , 33 :3182 , 1990
Abstract : A series of conformationally restricted analogues of the partial muscarinic agonist N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)acetamide (BM 5; 1) was synthesized. Three of the racemic derivatives were resolved into the enantiomers. The compounds were investigated for muscarinic and antimuscarinic activity in the isolated guinea pig ileum. They were found to be fairly potent muscarinic antagonists or weak partial agonists. The new compounds were either equally or less potent than 1 in inhibiting (-)-[3H]-N-methylscopolamine binding in homogenates of the rat cerebral cortex. Thus, structural modifications to 1 in which the amide moiety and the methyl group in the butynyl chain have been joined to form a six- or seven-membered ring preserve affinity but abolish efficacy. The R enantiomers were found to have 14-79 times higher affinity to ileal muscarinic receptors than the respective antipodes. The enantiomeric affinity ratios were nearly identical in both preparations studied. As suggested by molecular mechanics calculations, the difference in affinity between the five-membered and the six- and seven-membered ring analogues may be rationalized in conformational terms.
ESTHER : Lundkvist_1990_J.Med.Chem_33_3182
PubMedSearch : Lundkvist_1990_J.Med.Chem_33_3182
PubMedID: 2258904

Title : Antimuscarinic potency and functional selectivity of oxotremorine analogs at muscarinic receptor subtypes in the rat - Vargas_1990_Life.Sci_47_2065
Author(s) : Vargas HM , Ringdahl B
Ref : Life Sciences , 47 :2065 , 1990
Abstract : The potency of six antimuscarinic oxotremorine analogs at sympathetic ganglionic M1 and brainstem M2 muscarinic receptors was compared in the rat. Inhibition of the pressor effects of McNA343 or physostigmine was used as functional indicators of M1 and M2 blockade, respectively. 50% inhibitory doses (ID50) were calculated against both cholinomimetics. Of the analogs, PCA-10 was the most potent, with ID50 values of 0.16 and 0.11 mumol/kg versus McNA343 and physostigmine, respectively. A correlation analysis indicated that these analogs did not functionally discriminate between responses mediated by neuronal M1 or M2 muscarinic receptors in vivo. In contrast, these analogs antagonized M1 ganglionic responses at doses which produced negligible antagonism at cardiac and vascular M2 receptors.
ESTHER : Vargas_1990_Life.Sci_47_2065
PubMedSearch : Vargas_1990_Life.Sci_47_2065
PubMedID: 1703260

Title : Dimethylsulfonium analogues of the muscarinic agent McN-A-343: [4-[[N-(3- or 4-halophenyl)carbamoyl]oxy]-2-butynyl] dimethylsulfonium perchlorates - Mellin_1989_J.Med.Chem_32_1590
Author(s) : Mellin C , Vargas HM , Ringdahl B
Ref : Journal of Medicinal Chemistry , 32 :1590 , 1989
Abstract : Some 3- and 4-bromophenyl and dimethylsulfonium analogues of the muscarinic agent [4-[[N-(3-chlorophenyl)-carbamoyl]oxy]-2-butynyl] trimethylammonium chloride (McN-A-343) (1) were synthesized. The new compounds were assayed for effects on arterial blood pressure in the pithed rat (ganglionic muscarinic activity). The dimethylsulfonium salts (13a-d) appeared to be partial agonists in relation to 1. The 4-bromophenyl-substituted trimethylammonium iodide 10d exceeded 1 in potency by 3-fold. The compounds retained the selectivity for ganglionic muscarinic receptors shown by 1 since they had only weak effects on the guinea pig ileum in vitro.
ESTHER : Mellin_1989_J.Med.Chem_32_1590
PubMedSearch : Mellin_1989_J.Med.Chem_32_1590
PubMedID: 2472484

Title : Suppression of hypertension during chronic reduction of brain acetylcholine in spontaneously hypertensive rats - Vargas_1988_J.Hypertens_6_739
Author(s) : Vargas HM , Brezenoff HE
Ref : J Hypertens , 6 :739 , 1988
Abstract : Experiments were conducted to determine the effects of chronic depletion of brain acetylcholine (ACh) on the development and maintenance of hypertension in spontaneously hypertensive rats (SHR). Synthesis of brain ACh was inhibited by chronic infusion of hemicholinium-3 (HC-3) into the cerebral ventricles, and systolic blood pressure was monitored by tail cuff occlusion. In 5-week-old SHR, infusion of HC-3 (0.25 micrograms/h) suppressed development of hypertension when compared to saline-infused control SHR during the 21 days of infusion (140 versus 190 mmHg on day 21). Hypothalamic and brain-stem ACh during this period was reduced by 50% and by 60-75%, respectively. In 18-week-old SHR with established hypertension, HC-3 (0.25 and 0.5 micrograms/h) reduced systolic blood pressure by 35-40 mmHg for 8 days, after which pressures returned to control hypertensive levels (191 mmHg) by day 14. The increase in blood pressure was accompanied by recovery of hypothalamic ACh levels to 75% of control. The specificity and physiological effectiveness of HC-3 was shown by its ability to inhibit the centrally mediated pressor response to physostigmine but not to oxotremorine. Infusion of HC-3 did not affect body growth, water consumption, body temperature or gross behavior. From this study, it can be concluded that brain cholinergic neurons are an important component in the development and the maintenance of hypertension in the SHR.
ESTHER : Vargas_1988_J.Hypertens_6_739
PubMedSearch : Vargas_1988_J.Hypertens_6_739
PubMedID: 3183376