Clinical aspects of dopamine agonists and antagonists.

Dopamine and its specific receptors are widely distributed in man. Body regions where dopaminergic activity is of special pharmacologic interest include the basal ganglions, hypothalamus, chemoreceptor trigger zone, other less well defined areas in the central nervous system, and the renal and cardiovascular systems. The search for dopaminergic agents to modify these systems in disease states has depended heavily on in vitro and in vivo bioassays. These assays involving receptor binding, enzyme activation, smooth muscle and neuronal excitation, and modification of animal behavior have provided physicians with important therapeutic tools. Indeed, the introduction of levodopa for the treatment of Parkinson's disease and of the phenothiazines and related drugs for schizophrenia and psychosis has been a hallmark of neuropharmacologic research. However, the maximal benefits that these drugs may afford have not yet been realized due to an inadequate understanding of disease processes and a relative lack of specificity of drug action.     

Neuroprotective effect of atypical antipsychotics in cognitive and non-cognitive behavioral impairment in animal models

Antipsychotic drugs are divided into two groups: typical and atypical. Recent clinical studies show atypical antipsychotics have advantages over typical antipsychotics in a wide variety of neuropsychiatric conditions, in terms of greater efficacy for positive and negative symptoms, beneficial effects on cognitive functioning, and fewer extra pyramidal side effects in treating schizophrenia. As such, atypical antipsychotics may be effective in the treatment of depressive symptoms associated with psychotic and mood disorders, posttraumatic stress disorder, and psychosis in Alzheimer’s disease. In this paper, we describe the effects and potential neurochemical mechanisms of action of atypical antipsychotics in several animal models showing memory impairments and/or non-cognitive behavioral changes. The data provide new insights into the mechanisms of action of atypical antipsychotics that may broaden their clinical applications.     

Thioesters for the in vitro evaluation of agents to image brain cholinesterases

Cholinesterases are associated with pathology characteristic of conditions such as Alzheimer’s disease and are therefore, considered targets for neuroimaging. Ester derivatives of N-methylpiperidinol are promising potential imaging agents; however, methodology is lacking for evaluating these compounds in vitro. Here, we report the synthesis and evaluation of a series of N-methylpiperidinyl thioesters, possessing comparable properties to their corresponding esters, which can be directly evaluated for cholinesterase kinetics and histochemical distribution in human brain tissue. N-methylpiperidinyl esters and thioesters were synthesized and they demonstrated comparable cholinesterase kinetics. Furthermore, thioesters were capable, using histochemical method, to visualize cholinesterase activity in human brain tissue. N-methylpiperidinyl thioesters can be rapidly evaluated for cholinesterase kinetics and visualization of enzyme distribution in brain tissue which may facilitate development of cholinesterase imaging agents for application to conditions such as Alzheimer’s disease.     

2-(2-indolyl-)-4(3H)-quinazolines derivates as new inhibitors of AChE: design,synthesis, biological evaluation and molecular modelling

We recently reported that synthetic derivatives of rutaecarpine alkaloid exhibited high acetyl cholinesterase (AChE) inhibitory activity and high selectivity for AChE over butyrylcholinesterases (BuChE). To explore novel effective drugs for the treatment of Alzheimer’s disease (AD), in this paper, further research results were presented. Starting from a structure-based drug design, a series of novel 2-(2-indolyl-)-4(3H)-quinazolines derivates were designed and synthesized as the ring-opened analogues of rutaecarpine alkaloid and subjected to pharmacological evaluation as AChE inhibitors. Among them, derivates 3a–c and 3g–h exhibited strong inhibitory activity for AChE and high selectivity for AChE over BuChE. The structure–activity relationships were discussed and their binding conformation and simultaneous interactions mode were further clarified by kinetic characterization and the molecular docking studies.     

Evidence of calmodulin involvement in cell volume recovery following hypo-osmotic stress

An influx of Ca2+ into red blood cells of the bivalve mollusc Noetia ponderosa occurs immediately following a hypo-osmotic stress. The volume recovery response to the stress is dependent upon [Ca2+]o and is inhibited by phenothiazines. The action of these drugs is on the amino acid regulation portion of the recovery rather than on the ionic portion. Since the phenothiazines are non-specific in action, we have conducted several experiments to decide the site of phenothiazine action on the volume recovery response. The sulfoxide derivatives of both chlorpromazine and trifluoperazine have no effect on volume regulation at the same dose where the parent compound inhibits. At 50-100 times the concentration of the parent compound, the derivatives block both volume regulation and taurine efflux. The phorbol ester, TPA, an activator of protein kinase C, alters the volume recovery, but does so by affecting K+ rather than amino acid regulation. The only phenothiazine target that we can not rule out is calmodulin, which we also demonstrate to be present in the clam red cells. Thus, the data presented suggest that calmodulin is involved in the amino acid regulatory portions of the volume recovery in response to hypo-osmotic swelling.     

Structure-activity relationships for inhibition of human cholinesterases by alkyl amide phenothiazine derivatives

Several lines of evidence indicate that inhibition of butyrylcholinesterase (BuChE) is important in the treatment of certain dementias. Further testing of this concept requires inhibitors that are both BuChE-selective and robust. N-alkyl derivatives (2, 3, 4) of phenothiazine (1) have previously been found to inhibit only BuChE in a mechanism involving pi-pi interaction between the phenothiazine tricyclic ring system and aromatic residues in the active site gorge. To explore features of phenothiazines that affect the selectivity and potency of BuChE inhibition, a series of N-carbonyl derivatives (5-25) was synthesized and examined for the ability to inhibit cholinesterases. Some of the synthesized derivatives also inhibited AChE through a different mechanism involving carbonyl interaction within the active site gorge. Binding of these derivatives takes place within the gorge, since this inhibition disappears when the molecular volume of the derivative exceeds the estimated active site gorge volume of this enzyme. In contrast, BuChE, with a much larger active site gorge, exhibited inhibition that increased directly with the molecular volumes of the derivatives. This study describes two distinct mechanisms for binding phenothiazine amide derivatives to BuChE and AChE. Molecular volume was found to be an important parameter for BuChE-specific inhibition.     

Development of acetophenone ligands as potential neuroimaging agents for cholinesterases

Association of cholinesterase with β-amyloid plaques and tau neurofibrillary tangles in Alzheimer’s disease offers an opportunity to detect disease pathology during life. Achieving this requires development of radiolabelled cholinesterase ligands with high enzyme affinity. Various fluorinated acetophenone derivatives bind to acetylcholinesterase with high affinity, including 2,2,2-trifluoro-1-(3-dimethylaminophenyl)ethanone (1) and 1-(3-tert-butylphenyl)-2,2,2-trifluoroethanone (2). Such compounds also offer potential for incorporation of radioactive fluorine (¹⁸F) for Positron Emission Tomography (PET) imaging of cholinesterases in association with Alzheimer’s disease pathology in the living brain. Here we describe the synthesis of two meta-substituted chlorodifluoroacetophenones using a Weinreb amide strategy and their rapid conversion to the corresponding trifluoro derivatives through nucleophilic substitution by fluoride ion, in a reaction amenable to incorporating ¹⁸F for PET imaging. In vitro kinetic analysis indicates tight binding of the trifluoro derivatives to cholinesterases. Compound 1 has a K_i value of 7 nM for acetylcholinesterase and 1300 nM for butyrylcholinesterase while for compound 2 these values are 0.4 nM and 26 nM, respectively. Tight binding of these compounds to cholinesterase encourages their development for PET imaging detection of cholinesterase associated with Alzheimer’s disease pathology.     

Molecular perception of interactions between bis(7)tacrine and cystamine-tacrine dimer with cholinesterases as the promising proposed agents for the treatment of Alzheimer’s disease

The infamous chronic neurodegenerative disease, Alzheimer’s, that starts with short-term memory loss and eventually leads to gradual bodily function decline which has been attributed to the deficiency in brain neurotransmitters, acetylcholine, and butylcholine. As a matter of fact, design of compounds that can inhibit cholinesterases activities (acetylcholinesterase and butylcholinesterase) has been introduced as an efficient method to treat Alzheimer’s. Among proposed compounds, bis(7)tacrine (B7T) is recognized as a noteworthy suppressor for Alzheimer’s disease. Recently a new analog of B7T, cystamine-tacrine dimer is offered as an agent to detain Alzheimer’s complications, even better than the parent compound. In this study, classical molecular dynamic simulations have been employed to take a closer look into the modes of interactions between the mentioned ligands and both cholinesterase enzymes. According to our obtained results, the structural differences in the target enzymes active sites result in different modes of interactions and inhibition potencies of the ligands against both enzymes. The obtained information can help to investigate those favorable fragments in the studied ligands skeletons that have raised the potency of the analog in comparison with the parent compound to design more potent multi target ligands to heal Alzheimer’s disease.     

Phenothiazine Poisoning A Review of 48 Cases

Of 48 cases of phenothiazine poisoning that were analyzed, 34 were attributed to suicide attempts, nine to accidental ingestion, and five to drug reactions.As outpatient treatment of schizophrenia increases, cases of over-dose with phenothiazine drugs may be expected to increase also.The prescribing of multiple phenothiazines and antidepressants is probably contributory to the occurrence of mixed drug ingestions.The symptoms and signs of phenothiazine poisoning are largely predictable if the atropine-like, alpha-blocking, quinidine-like, and extrapyramidal actions of phenothiazines are appreciated. Unexplainable tachypnea and paradoxical miosis were noted in severe cases.In one case in the study phenothiazine intoxication was present in the newborn infant of a schizophrenic mother.     

Synthesis,molecular modeling and evaluation of novel N′-2-(4-benzylpiperidin-/piperazin-1-yl)acylhydrazone derivatives as dual inhibitors for cholinesterases and Aβ aggregation

To develop new drugs for treatment of Alzheimer’s disease, a group of N′-2-(4-Benzylpiperidin-/piperazin-1-yl)acylhydrazones was designed, synthesized and tested for their ability to inhibit acetylcholinesterase, butyrylcholinesterase and aggregation of amyloid beta peptides (1–40, 1–42 and 1–40_1–42). The enzyme inhibition assay results indicated that compounds moderately inhibit both acetylcholinesterase and butyrylcholinesterase. β-Amyloid aggregation results showed that all compounds exhibited remarkable Aβ fibril aggregation inhibition activity with a nearly similar potential as the reference compound rifampicin, which makes them promising anti-Alzheimer drug candidates. Docking experiments were carried out with the aim to understand the interactions of the most active compounds with the active site of the cholinesterase enzymes.     

Molecular and cellular mechanisms of sporadic Alzheimer’s disease: Studies on rodent models <Emphasis Type="Italic">in vivo</Emphasis>

In this review, recent data are presented on molecular and cellular mechanisms of pathogenesis of the most widespread (about 95%) sporadic forms of Alzheimer’s disease obtained on in vivo rodent models. Although none of the available models can fully reproduce the human disease, several key molecular mechanisms (such as dysfunction of neurotransmitter systems, especially of the acetylcholinergic system, β-amyloid toxicity, oxidative stress, neuroinflammation, mitochondrial dysfunction, disturbances in neurotrophic systems) are confirmed with different models. Injection models, olfactory bulbectomy, and senescence accelerated OXYS rats are reviewed in detail. These three approaches to in vivo modeling of sporadic Alzheimer’s disease have demonstrated a considerable similarity in molecular and cellular mechanisms of pathology development. Studies on these models provide complementary data, and each model possesses its specific advantages. A general analysis of the data reported for the three models provides a multifaceted and the currently most complete molecular picture of sporadic Alzheimer’s disease. This is highly relevant also from the practical viewpoint because it creates a basis for elaboration and preclinical studies of means for treatment of this disease.     

Determination of the molar absorptivities of phenothiazine cation radicals generated by oxidation with hydrogen peroxide/peroxidase.

Phenothiazines are used as antipsychotic drugs and as reagents to determine microamounts of hemoglobin in biological fluids and tissues. Several agents cause the oxidation of phenothiazines to chromophoric cation radicals, whose stability may be related with their biological action. Enzymes and proteins with peroxidase activity catalyze the oxidation by H2O2 of phenothiazines to their corresponding cation radicals, which suffer a nonenzymatic breakdown. The instability of these cation radicals makes the determination of their respective molar absorptivities very difficult. These properties, however, have been determined for a few phenothiazine cation radicals by cumbersome or unreliable procedures. In this paper a new method is proposed and applied to six different phenothiazines oxidized with H2O2/peroxidase. The method involves the stoichiometric exhaustion of H2O2, under assay conditions which yield a fast enzymatic formation of phenothiazine cation radicals and which slow down their nonenzymatic breakdown. This method may be useful for quantitative studies on the enzymatic activity and the reaction mechanism of the oxidation of a number of phenothiazines catalyzed by different types of peroxidase, as well as by proteins with peroxidase activity, such as hemoglobin.     

Synthesis and application of β-carbolines as novel multi-functional anti-Alzheimer’s disease agents

The design, synthesis and assessment of β-carboline core-based compounds as potential multifunctional agents against several processes that are believed to play a significant role in Alzheimer’s disease (AD) pathology, are described. The activity of the compounds was determined in Aβ self-assembly (fibril and oligomer formation) and cholinesterase (AChE, BuChE) activity inhibition, and their antioxidant properties were also assessed. To obtain insight into the mode of action of the compounds, HR-MS studies were carried out on the inhibitor-Aβ complex formation and molecular docking was performed on inhibitor-BuChE interactions. While several compounds exhibited strong activities in individual assays, compound 14 emerged as a promising multi-target lead for the further structure-activity relationship studies.     

Neuroprotective effect of atypical antipsychotics in cognitive and non-cognitive behavioral impairment in animal models

Antipsychotic drugs are divided into two groups: typical and atypical. Recent clinical studies show atypical antipsychotics have advantages over typical antipsychotics in a wide variety of neuropsychiatric conditions, in terms of greater efficacy for positive and negative symptoms, beneficial effects on cognitive functioning, and fewer extra pyramidal side effects in treating schizophrenia. As such, atypical antipsychotics may be effective in the treatment of depressive symptoms associated with psychotic and mood disorders, posttraumatic stress disorder and psychosis in Alzheimer disease. In this paper, we describe the effects and potential neurochemical mechanisms of action of atypical antipsychotics in several animal models showing memory impairments and/or non-cognitive behavioral changes. The data provide new insights into the mechanisms of action of atypical antipsychotics that may broaden their clinical applications.Key words: atypical antipsychotics, neuroprotective effect, memory, anxiety-like behavior, neurotoxicity     

Ethyl nitrobenzoate: A novel scaffold for cholinesterase inhibition

A series of novel cholinesterase inhibitors containing nitrobenzoate core structure were synthesized by a facile and efficient method. The structure of the novel compounds were fully characterized and confirmed by analytical as well as spectroscopic methods. Compound indicated as 2f was found to possess the best cholinesterase inhibitory activities of all the evaluated compounds. Results suggest that 2f is a selective acetylcholinesterase inhibitor, although it also inhibits butyrylcholinesterase at higher concentration. Kinetics inhibition result suggest that 2f is a mixed-mode inhibitor of acetylcholinesterase. In addition, it was found to have low cytotoxicity. Molecular docking on compound 2f was carried out to rationalize the observed in vitro enzymatic assay results. Most importantly, the potential of nitrobenzoate derivatives as cholinesterase inhibitor was shown through this study. In summary, we discovered nitrobenzoates as a new scaffold that may eventually yield useful compounds in treatment of Alzheimer’s disease.     

Genetic interactions found between calcium channel genes modulate amyloid load measured by positron emission tomography

Late-onset Alzheimer’s disease (LOAD) is known to have a complex, oligogenic etiology, with considerable genetic heterogeneity. We investigated the influence of genetic interactions between genes in the Alzheimer’s disease (AD) pathway on amyloid-beta (Aβ) deposition as measured by PiB or AV-45 ligand positron emission tomography (PET) to aid in understanding LOAD’s genetic etiology. Subsets of the Alzheimer’s Disease Neuroimaging Initiative (ADNI) cohorts were used for discovery and for two independent validation analyses. A significant interaction between RYR3 and CACNA1C was confirmed in all three of the independent ADNI datasets. Both genes encode calcium channels expressed in the brain. The results shown here support previous animal studies implicating interactions between these calcium channels in amyloidogenesis and suggest that the pathological cascade of this disease may be modified by interactions in the amyloid–calcium axis. Future work focusing on the mechanisms of such relationships may inform targets for clinical intervention.     

Isothiocyanates: cholinesterase inhibiting,antioxidant, and anti-inflammatory activity

Finding a new type of cholinesterase inhibitor that would overcome the brain availability and pharmacokinetic parameters or hepatotoxic liability has been a focus of investigations dealing with the treatment of Alzheimer’s disease. Isothiocyanates have not been previously investigated as potential cholinesterase inhibitors. These compounds can be naturally produced from their glucosinolate precursors, secondary metabolites widely distributed in our daily Brassica vegetables. Among 11 tested compounds, phenyl isothiocyanate and its derivatives showed the most promising inhibitory activity. 2-Methoxyphenyl ITC showed best inhibition on acetylcholinesterase with IC₅₀ of 0.57?mM, while 3-methoxyphenyl ITC showed the best inhibition on butyrylcholinesterase having 49.2% at 1.14?mM. Assessment of the antioxidant efficacy using different methods led to a similar conclusion. The anti-inflammatory activity was also tested using human COX-2 enzyme, ranking phenyl isothiocyanate, and 3-methoxyphenyl isothiocyanate as most active, with ～99% inhibition at 50?μM.     

Novel conjugates of tacrine with 1,2,4,-thiadiazole as highly effective cholinesterase inhibitors,blockers of NMDA receptors,and antioxidants

Conjugates of tacrine with 1,2,4-thiadiazole derivatives were synthesized for the first time. Their esterase profile and effects on the key NMDA receptor-binding sites as well as antioxidant activity were investigated. The obtained compounds effectively inhibited cholinesterases (with a predominant effect on butyrylcholinesterase), simultaneously blocked two NMDA receptor-binding sites (allosteric and intrachannel sites, and exhibited a high radical-scavenging activity. Our study shows that the obtained compounds are promising to design drugs for the treatment of Alzheimer’s disease and other multifactorial neurodegenerative diseases.     

NMDA receptor as a newly identified member of the metabotropic glutamate receptor family: Clinical implications for neurodegenerative diseases

Recent reports have proposed a novel function for the N-methyl-d-aspartate (NMDA) receptor (NMDAR), a well-known excitatory, ionotropic receptor. A series of observations employing pharmacological techniques has proposed that upon ligand binding, this ionotropic receptor can actually function via signaling cascades independent of traditional ionotropic action. Moreover, the “metabotropic” action of NMDARs is suggested to mediate a form of synaptic plasticity, namely long-term synaptic depression (LTD), which shares cellular mechanisms with the synaptic deficits observed in Alzheimer’s disease. Given that a growing body of clinical and preclinical evidence strongly recommends NMDAR antagonists for their therapeutic potentials and advantages in a variety of diseases, further investigation into their molecular and cellular mechanisms is required to better understand the “metabotropic” action of NMDARs.