Novel therapy for Alzheimer's disease.

Recent results support the hypothesis that microglia and/or macrophages of the brain, by producing oxidants, could play a role in the local inactivation of the Kunitz protease inhibitor (KPI) domain of beta-amyloid precursor protein (APP), thereby facilitating deposition of abnormal amyloid filaments in patients with Alzheimer's disease (AD). Protease inhibitors and/or free radical scavengers might serve as therapy for the amyloidosis of AD.

Ginkgo biloba extract (EGb 761) and CNS functions: basic studies and clinical applications.

The effects of EGb 761 on the CNS underlie one of its major therapeutic indications; i.e., individuals suffering from deteriorating cerebral mechanisms related to age-associated impairments of memory, attention and other cognitive functions. EGb 761 is currently used as symptomatic treatment for cerebral insufficiency that occurs during normal ageing or which may be due to degenerative dementia, vascular dementia or mixed forms of both, and for neurosensory disturbances. Depressive symptoms of patients with Alzheimer's disease (AD) and aged non-Alzheimer patients may also respond to treatment with EGb 761 since this extract has an "anti-stress" effect. Basic and clinical studies, conducted both in vitro and in vivo, support these beneficial neuroprotective effects of EGb 761. EGb 761 has several major actions; it enhances cognition, improves blood rheology and tissue metabolism, and opposes the detrimental effects of ischaemia. Several mechanisms of action are useful in explaining how EGb 761 benefits patients with AD and other age-related, neurodegenerative disorders. In animals, EGb 761 possesses antioxidant and free radical-scavenging activities, it reverses age-related losses in brain alpha 1-adrenergic, 5-HT1A and muscarinic receptors, protects against ischaemic neuronal death, preserves the function of the hippocampal mossy fiber system, increases hippocampal high-affinity choline uptake, inhibits the down-regulation of hippocampal glucocorticoid receptors, enhances neuronal plasticity, and counteracts the cognitive deficits that follow stress or traumatic brain injury. Identified chemical constituents of EGb 761 have been associated with certain actions. Both flavonoid and ginkgolide constituents are involved in the free radical-scavenging and antioxidant effects of EGb 761 which decrease tissue levels of reactive oxygen species (ROS) and inhibit membrane lipid peroxidation. Regarding EGb 761-induced regulation of cerebral glucose utilization, bilobalide increases the respiratory control ratio of mitochondria by protecting against uncoupling of oxidative phosphorylation, thereby increasing ATP levels, a result that is supported by the finding that bilobalide increases the expression of the mitochondrial DNA-encoded COX III subunit of cytochrome oxidase. With regard to its "anti-stress" effect, EGb 761 acts via its ginkgolide constituents to decrease the expression of the peripheral benzodiazepine receptor (PBR) of the adrenal cortex.

Activation of prostacyclin synthesis in cultured aortic smooth muscle cells by 'diuretic-antihypertensive' drugs.

In cultured smooth muscle cells of rat aorta, four diuretic agents, furosemide, bumetanide, cicletanide and piretanide (all at 10(-6)-10(-5) M), significantly enhanced the transformation of exogenously added arachidonic acid (AA) to prostacyclin. Studies with cultured smooth muscle cells and human leukocytes revealed that these same agents failed to inhibit lipoxygenase pathways. Taken together, these results indicate that the diuretic properties of these agents might be associated with a general activation of the AA cascade.

Effect of di-n-propylacetate on the 'binding of GABA to synaptosome-enriched fraction of rat cerebral cortex.

The effect of di-n-propylacetate (DPA) on the 'binding' of gamma-aminobutyric acid (GABA) to a synaptosome-enriched fraction of rat cerebral cortex has been examined using differential centrifugation and double-isotope liquid scintillation spectrometry. DPA at 10(-4) M caused a slight decrease in GABA binding. This effect could explain in part the in vivo anticonvulsant and behavioral effects of this drug when administered to animals in high systemic doses.

GABA and "neuro-cardiovascular" mechanisms.

One has only to recall that GABA appears to be a major inhibitory neurotransmitter in the vertebrate central nervous system (CNS), that it exerts a hypotensive action upon systemic administration, that it is present in the blood, that its actions are antagonized by bicuculline and picrotoxin and facilitated by benzodiazepines, and that receptors for GABA exist in cerebral blood vessels, to consider that GABA is somehow involved in cardiovascular regulation. One might even postulate that influences upon GABA-ergic mechanisms are involved in that dangerous sequence of biological activities: environmental stress ? anxiety ? atherosclerosis and hypertension, the latter of which represent major health problems of man. Herein, some evidence that appears to support this view will be presented.

Central GABA-ergic systems and feeding behavior.

Central GABA-ergic systems appear to be involved in the regulation of food intake and body weight in animals. Studies performed with systemic or intracerebral administration of GABA, GABA-agonists and GABA-antagonists support this view.

Do different populations of GABA-receptors exist in the vertebrate CNS?

Studies of the possible multiplicity of GABA-receptors that have been conducted with ligand-binding techniques and with certain electrophysiological and behavioral methods have been reviewed and analyzed. It seems evident that different populations of GABA binding sites exist in subcellular preparations of CNS tissues, but it is not yet certain that these sites reflect different populations of GABA-receptors that might exist in vivo.

Effects of psychoactive agents on GABA binding processes.

Recent in vitro studies have revealed that benzodiazepines, opiates, barbiturates and ethanol might influence GABA binding to CNS membrane sites. Further studies of such interactions might be helpful for explaining both the mechanisms of action of these psychoactive agents and the tolerance/dependence that might result from their continued use.

GABA and endocrine regulation-Relation to neurologic-psychiatric disorders.

Data obtained with experimental animals and with humans concerning the involvement of GABA-ergic systems in the control of hormonal secretion have been discussed and analyzed. The available evidence indicates that GABA-ergic systems might modulate the release of several hypothalamic-hypophyseal hormones that are involved in behavioral regulation, either via their endocrine actions or via their direct actions on the brain. Further studies along this line might lead to the development of GABA-ergic drugs that will be useful for treating certain hormonal or neuropsychiatric disorders.

Interactions of verapamil, D 600, flunarizine and nifedipine with cerebral histamine-receptors.

Experiments conducted on membrane fractions of guinea-pig brain using ligand-binding techniques have shown that certain Ca(2+)-antagonists interact with histamine (H(1) or H(2)) receptors. Flunarizine (inhibition constant, K(i) ? 86 nM) was nearly as potent as diphenhydramine (K(i) ? 44 nM) in inhibiting [(3)H]pyrilamine binding to cerebellar H(1)-receptors, whereas verapamil, D 600 and nifedipine did not interact with this site. Regarding [(3)H]tiotidine binding to H(2)-receptors of cerebral cortex, verapamil (K(i) ? 1400 nM) and D 600 (K(i) ? 1240 nM) were nearly as potent as cimetidine (K(i) ? 910 nM) whereas flunarizine and nifedipine were inactive. The interaction of flunarizine with H(1)-receptors might explain, in part, its sedative side-effect. The interaction of verapamil with H(2)-receptors, demonstrated here for the first time, might be involved in the anti-arrhythmic action of this agent.

Competitive inhibition of 5-HT receptors in rabbit isolated aorta by the Ca(2+)-antagonist methoxyverapamil (D 600).

Experiments conducted with rabbit isolated aorta have revealed that the Ca(2+)-antagonist 3-methoxy-verapamil (D 600) is a potent competitive antagonist of the contractile action of 5-HT. Thus, the anti-hypertensive action of D 600, as well as some of its side effects, could be related to its antagonism of 5-HT receptors. D 600 might be useful in neurochemical and neurophysiological experiments that are aimed at examining 5-HT receptors, as well as in treating certain cerebrovascular disorders of man (e.g., migraine).

Separate binding sites in rat brain synaptic membranes for l-cysteine sulfinate and for l-glutamate.

Binding of l-[(3)H]cysteine sulfinic acid (CSA) and l-[(3)H]glutamate were compared in various subcellular fractions and in the presence of a variety of pharmacological and ionic manipulations in order to test the possibility that the two amino acids possessed separate binding sites. The specific l-[(3)H]cysteine sulfinate binding was found to be enriched maximally in medium and high density synaptic membranes, while the crude mitochondrial synaptosomal fraction displayed the highest l-[(3)H]glutamate binding. The ratio of l-[(3)H]cysteine sulfinate binding/l-[(3)H]glutamate binding was variable across brain regions. Several compounds differentially affected l-[(3)H]cysteine sulfinate and l-[(3)H]glutamate binding. l-cysteine sulfinate was the most potent displacer regardless of the binding considered. Finally, while cations produced qualitatively similar effects on the binding of the two amino acids, quantitative differences were evident. In sum, these data revealed the complexity of l-[(3)H]cysteine sulfinate and l-[(3)H]glutamate binding. They suggest the existence of several binding sites and that some of these are shared by both substances. However, the results also indicate that separate binding sites for the two amino acids exist in synaptic membrane, giving further support to the hypothesis that cysteine sulfinate serves a neurotransmitter role in the central nervous system.

High-affinity binding of [3H]muscimol to subcellular particles of a neurone-enriched culture of embryonic rat brain.

High-affinity, Na+-independent binding of [3H]muscimol (KB approximately equal to 1.6 x 10(-8) M; Bmax approximately equal to 0.14 nmol/g pellet) occurred to a frozen-thawed particulate fraction of 74-h-old neurone-enriched cultures prepared from the cerebra of 12-13-day-old rat embryos. This finding provides evidence that GABA-receptors exist on cultured neurones which contain only a few synaptic connections.

gamma-Aminobutyric acid-ergic analgesia: implications for gamma-aminobutyric acid-ergic therapy for drug addictions.

Recent in vivo and in vitro studies regarding the involvement of gamma-aminobutyric acid (GABA)-ergic systems in analgesia and in opiate dependence have been reviewed and analyzed. It seems evident that GABA-ergic systems play a role in mediating the effects of opiates and that some interplay might exist between endogenous opioid systems and GABA-ergic systems. Systemic administration of GABA-agonists, GABA uptake blockers and inhibitors of GABA-alpha-oxoglutarate transaminase (GABA-T) can produce potent analgesic actions in experimental animals and in man. Further study of such agents might lead to the development of new analgesics and/or new drugs for treating certain types of drug addiction.

Coronary atherosclerosis: current therapeutic approaches and future trends.

Invasive cardiovascular procedures, such as percutaneous translumenal coronary angioplasty (PTCA) and aorto-coronary bypass surgery (ACBS), that are currently employed in treating the coronary stenosis or occlusion caused by atherosclerosis represent a major therapeutic advance for managing coronary heart disease (CHD). However, the cellular proliferative response and associated intimal hyperplasia that can follow the damage to blood vessels that occurs with these procedures leads to late complications which cannot be effectively controlled by presently available drugs. Hence, a new approach is required for managing these complications, termed "restenosis" (in the case of PTCA) or "stenosis" (in the case of ACBS). Existing drug therapy is reviewed and some new approaches to this problem are provided herein. Further studies of growth factors and other substances that influence the cellular proliferative response that follows injury to the blood vessel wall could lead to the development of effective therapy. Inhibition of intimal hyperplasia and/or acceleration of endothelial cell re-growth provide a basis for such new approaches. Platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), as well as endothelium-derived relaxing factor(s) (EDRF) and calcitonin gene-related peptide (CGRP) are among the substances discussed. Modification of certain currently available drugs (e.g. Ca(2+)-antagonists) could also be of value in meeting this therapeutic demand.

The brain is protected from nutrient excess.

Except for L-DOPA, treatment of patients with large doses of neurotransmitter-precursors has not provided acceptable therapy for neurologic or psychiatric disorders. Indeed, neurophysiological effects generally have not followed changes in brain concentrations of the precursors or their products. A major reason for this ineffectiveness of precursor-loading may involve the very high metabolic activity of cerebrovascular endothelial cells, which can metabolize the precursor or its products before these reach the brain parenchyma. It is also noteworthy that studies purporting to examine the transport of precursors across the "blood-brain barrier" actually may not measure transport as such but rather the disappearance of precursor from the blood. The metabolic effects of the endothelial cell barrier itself would have greatly influence such studies and, heretofore, have been ignored. Thus, transport indices calculated from such experiments may need re-evaluation. Even when nutrients (precursors) are present in the blood in such excess that they do traverse the endothelial "blood-brain barrier" and enter the brain's interstitial space, other mechanisms (e.g., intraneuronal degradation) likely prevent these substances from exerting neurophysiological effects.

Pharmacological studies of somatostatin and somatostatin-analogues: therapeutic advances and perspectives.

This article is aimed at reviewing and analyzing studies that are related to the possible therapeutic use of a potent and ubiquitously-distributed hormone--somato-statin (SS-14), and its analogues. Administration of these substances has provided beneficial effects in treating acromegaly, gastro-intestinal hemorrhagic and hypersecretory disorders, acute pancreatitis, diabetes mellitus, and certain types of cancer. Further studies with SS-14-analogues might provide new therapies for treating certain life-threatening disorders of man.

Further characterization of the anorexic action of orally-administered THIP, a GABA-analogue, in the rat.

Sprague-Dawley rats were used to further characterize the anorexic action of orally-administered THIP, a GABA-analogue. The anorexic action of THIP (5 or 10 mg/kg) was antagonized by prior subcutaneous injection of bicuculline (1 mg/kg), but not by prior subcutaneous injection of bicuculline-methobromide (1.5 mg/kg), strychnine-SO4 (0.75 mg/kg), pentylenetetrazol (25 mg/kg), or picrotoxin (1 mg/kg). Orally-administered GABA (50-300 mg/kg), bicuculline (1-10 mg/kg) or picrotoxin (1-10 mg/kg) generally did not inhibit food intake. These results indicate that the anorexic action of THIP is mediated by central GABA-receptors.

Interactions of Ginkgo biloba extract (EGb 761), diazepam and ethyl beta-carboline-3-carboxylate on social behavior of the rat.

The social interaction test was used to examine the effects of an extract of Ginkgo biloba (EGb 761) and its possible interactions with diazepam and ethyl beta-carboline-3-carboxylate (beta-CCE). Pairs of naive (unfamiliar) male Wistar AF rats subjected to the same treatment were placed in a novel test arena that was brightly illuminated, and the duration (in s) of social contact was observed over a 10 min period. Single injections of EGb 761 (8-16 mg/kg, i.p.), given 30 min prior to testing, or repeated oral administration of the extract (48 or 96 mg/kg/day) for 8 days, significantly decreased social contact under conditions that did not influence locomotor activity. Injection of diazepam (1 mg/kg, i.p.), 30 min before testing, significantly increased social contact. Injection of diazepam to animals that had received repeated oral treatment with EGb 761 (96 mg/kg/ day) increased social interaction to an extent greater than observed with diazepam alone. Injection of beta-CCE (2-16 mg/kg, i.p.), 15 min before testing, significantly decreased social contact. When the animals were treated with EGb 761 (48 or 96 mg/kg/day, p.o. for 8 days) and beta-CCE (4 mg/kg), both of which decreased social interaction when administered alone, the resulting level of social contact was similar to that of control animals. Interactions with certain sites of central GABAA/ benzodiazepine/Cl- channel receptor complexes could be involved in mediating these effects of EGb 761, diazepam and beta-CCE.

Mechanism of endothelium-dependent vasorelaxation.

A sequential mechanism for endothelium-dependent vasorelaxation is proposed. The following events appear to be involved: Endothelial cell: activation of a receptor----activation of membrane phospholipases----increase in intracellular free Ca2+----formation of endothelium-derived relaxing factor(s) (EDRF) via a cytochrome P450-dependent epoxygenase or non-enzymatic lipid peroxidation pathway----release of EDRF----diffusion of EDRF to the smooth muscle cell; Smooth muscle cell: activation of guanyl cyclase----activation of protein kinase----protein phosphorylation----dephosphorylation of myosin light chain----relaxation. Relationships between endothelium-dependent and endothelium-independent vasorelaxation are indicated. EDRF-candidates include aldehydes and epoxides.