Design, synthesis, molecular modeling and neuroprotective effects of a new framework of cholinesterase inhibitors for Alzheimer's disease.

In search of a novel class of compounds against Alzheimer's disease (AD), a new series of 7-chloro-aminoquinoline derivatives containing methylene spacers of different sizes between the 7-chloro-4-aminoquinoline nucleus and imino methyl substituted phenolic rings, and also their reduced analogues, were designed, synthesized and evaluated as neuroprotective agents for AD in vitro. In spite of the multifaceted feature of AD, cholinesterases continue to be powerful and substantial targets, as their inhibition increases both the level and duration of the acetylcholine neurotransmitter action. The compounds presented inhibitory activity in the micromolar range against acetylcholinesterase (AChE) (imines and amines) and butyrylcholineterase (BChE) (amines). The SAR study revealed that elongation of the imine side chain improved AChE activity, whereas the reduction of these compounds to amines was crucial for higher activity and indispensable for BChE inhibition. The most promising selective inhibitors were not cytotoxic and did not stimulate pro-inflammatory activity in glial cells. Kinetic and molecular modeling studies indicated that they also show mixed-type inhibition for both enzymes, behaving as dual-site inhibitors, which can interact with both the peripheral anionic site and the catalytic anionic site of AChE. They could therefore restore cholinergic transmission and also may inhibit the aggregation of Aß promoted by AChE. Additionally, one compound showed promising anti-inflammatory activity by reducing the microglial release of NO• at a concentration that is equivalent to the IC50 against BChE (30.32 ± 0.18 µM) and 15-fold greater than the IC50 against AChE (1.97 ± 0.20 µM).Communicated by Ramaswamy H. Sarma.

Geissoschizoline, a promising alkaloid for Alzheimer's disease: Inhibition of human cholinesterases, anti-inflammatory effects and molecular docking.

Due to the lack of effective pharmacotherapy options to treats Alzheimer's disease, new strategies have been approached in the search for multi-target molecules as therapeutic options. In this work, four indole alkaloids, geissoschizoline, geissoschizone, geissospermine, and 3',4',5',6'-tetradehydrogeissospermine were isolated from Geissospermum vellosii (Pao pereira) and evaluated for their anticholinesterase activities. While geissospermine inhibited only butyrylcholinesterase (BChE), the other alkaloids behaved as non-selective inhibitors of acetylcholinesterase (AChE) and BChE. In cell viability tests, only geissoschizoline was not cytotoxic. Therefore, geissoschizoline actions were also evaluated in human cholinesterases, where it was twice as potent inhibitor of hBChE (IC50 = 10.21 ± 0.01 µM) than hAChE (IC50 = 20.40 ± 0.93 µM). On enzyme kinetic studies, geissoschizoline presented a mixed-type inhibition mechanism for both enzymes. Molecular docking studies pointed interactions of geissoschizoline with active site and peripheral anionic site of hAChE and hBChE, indicating a dual site inhibitor profile. Moreover, geissoschizoline also played a promising anti-inflammatory role, reducing microglial release of NO and TNF-α at a concentration (1 µM) ten and twenty times lower than the IC50 values of hBChE and hAChE inhibition, respectively. These actions give geissoschizoline a strong neuroprotective character. In addition, the ability to inhibit hAChE and hBChE, with approximate inhibitory potencies, accredits this alkaloid for therapeutic use in the moderate to severe phase of AD. Thus, geissoschizoline emerges as a possible multi-target prototype that can be very useful in preventing neurodegeneration and restore neurotransmission.

In-vitro evaluation studies of 7-chloro-4-aminoquinoline Schiff bases and their copper complexes as cholinesterase inhibitors.

Alzheimer's disease (AD) is one of the most common age-related neurodegenerative disorders. Aggregation of amyloid-ß peptide into extracellular plaques with incorporation of metal ions, such as Cu2+, and reduction of the neurotransmitter acetylcholine levels are among the factors associated to the AD brain. Hence, a series of 7-chloro-4-aminoquinoline Schiff bases (HLa-e) were synthesized and their cytotoxicity and anti-cholinesterase activity, assessed for Alzheimer's disease. The intrinsic relationship between Cu2+ and the amyloidogenic plaques encouraged us to investigate the chelating ability of HLa-e. Dimeric tetracationic compounds, [Cu2(NHLa-e)4]Cl4, containing quinoline protonated ligands were isolated from the reactions with CuCl2·2H2O and fully characterized in the solid state, including an X ray diffraction study, whereas EPR data showed that the complexes exist as monomers in DMSO solution. The inhibitory activity of all compounds was evaluated by Ellman's spectrophotometric method in acetylcholinesterase (AChE) from Electrophorus electricus and butyrylcholinesterase (BChE) from equine serum. HLa-e and [Cu(NHLd)2]Cl2 were selective for AChE (IC50 = 4.61-9.31 µM) and were not neurotoxic in primary brain cultures. Docking and molecular dynamics studies of HLa-e inside AChE were performed and the results suggested that these compounds are able to bind inside AChE similarly to other AChE inhibitors, such as donepezil. Studies of the affinity of HLd for Cu2+ in DMSO/HEPES at pH 6.6 and pH 7.4 in µM concentrations showed formation of analogous 1:2 Cu2+/ligand complexes, which may suggest that in the AD-affected brain HLd may scavenge Cu2+ and the complex, also inhibit AChE.

Quantification through TLC-densitometric analysis, repellency and anticholinesterase activity of the homemade extract of Indian cloves.

The rise of the mosquitoes-transmitted diseases, like dengue, zika and chikungunya in Brazil in the last years has increased concerns on protection against mosquitoes bites. However, the prohibitive prices of the commercially available repellents for the majority of the Brazilian population has provoked a search for cheaper solutions, like the use of the homemade ethanolic extract of Indian clove (Syzygium aromaticum L.) as repellent, which has been reported as quite efficient by the local press. In order to verify this, we performed here the quantification of the main components of this extract through high-performance thin-layer chromatography (HPTLC)-densitometry and evaluated its efficiency as a repellent and its acetylcholinesterase (AChE) inhibition capacity. Our results have proved HPTLC-densitometry as an efficient and appropriate method for this quantification and confirmed the repellency activity, as well as its capacity of AChE inhibition.

Antinociceptive and anti-inflammatory effects of a Geissospermum vellosii stem bark fraction.

Geissospermum vellosii (Pao pereira) is a Brazilian tree whose stem barks are rich in indole alkaloids that present intense anticholinesterase activity. The present study evaluated the effects of a stem bark fraction (PPAC fraction) and ethanolic extract (EE) of Pao pereira in classic murine models of inflammation and pain. The EE and PPAC fraction, both at a dose of 30 mg/kg, significantly reduced mice abdominal constriction induced by acetic acid by 34.8% and 47.5%, respectively. In the formalin test, EE (30 mg/kg) and PPAC fraction (30 and 60 mg/kg) inhibited only the second phase, by 82.8%, 84.9% and 100%, respectively. Compared with indomethacin, similar doses of EE or PPAC fraction were approximately twice as effective in causing antinociception. PPAC fraction was not effective in the hot plate test but reduced the inflammatory response at the second (50.6%) and third (57.8%) hours of rat paw edema induced by carrageenan. Antihyperalgesic activity was observed within 30 min with a peak at 2 h (60.1%). These results demonstrate that compounds in PPAC fraction have anti-inflammatory and antinociceptive activity by a mechanism apparently unrelated to the opioid system. Regardless of similar responses to indomethacin, the effects of PPAC fraction are mainly attributed to acetylcholine actions.

Pereirina: o primeiro alcaloide isolado no Brasil? / Was pereirina the first alkaloid isolated in Brazil?

O artigo descreve a história da pereirina, um alcaloide extraído das cascas da Geissospermum vellosii Allemão, uma espécie de planta brasileira da família Apocynaceae, conhecida popularmente como Pau-pereira. A classificação botânica desta espécie e o emprego da pereirina na medicina popular foram as razões que acirraram a disputa entre os farmacêuticos brasileiros e estrangeiros pela glória de sua descoberta no Brasil do século XIX. Neste estudo constatou-se que a glória desta descoberta é do farmacêutico brasileiro Ezequiel Corrêa dos Santos e desta maneira, a pereirina é o primeiro alcaloide isolado no Brasil. As cascas do Pau-pereira foram, durante dois séculos, um importante remédio no combate a diversas doenças, devido às propriedades terapêuticas dos alcaloides presentes nas cascas da espécie e atualmente pesquisas estão sendo realizadas para comprovação científica de sua eficácia no combate a doenças virais como Aids, herpes e hepatite C.

This article describes the history of pereirina, an alkaloid extracted from Geissospermum vellosii Allemão barks, a Brazilian plant of Apocynaceae's family, popularly known as "pau-pereira". The botanical classification of this species and the use of pereirina in popular medicine were reasons for controversies and irritated disputes for the glory of the discovery among Brazilians and foreigners pharmacists. For two centuries, the pau-pereira's barks were important remedy to combat various diseases, because the therapeutic properties of alkaloids present in the barks of the species. The currently researches are being carried out for scientific proof of its effectiveness in combating viral diseases such as AIDS, herpes and hepatitis C.

Geissospermum vellosii stembark: anticholinesterase activity and improvement of scopolamine-induced memory deficits.

This study evaluated the cholinesterase inhibitory activity of an alkaloid-rich fraction of stembark from Geissospermum vellosii (PP), and its effect on memory tests in mice. PP inhibited rat brain and electric eel acetylcholinesterase, as well as horse serum butyrylcholinesterase in a concentration-dependent manner with mean IC(50) values of 39.3 microg/mL, 2.9 microg/mL, and 1.6 microg/mL, respectively. The main alkaloid with anticholinesterase activity in PP was isolated and identified as geissospermine. PP significantly reduced scopolamine-induced amnesia in the passive avoidance and Morris water maze tests, at 30 mg/kg i.p. (given 45 min before the test sessions). At the highest effective dose (60 mg/kg), administration of PP did not result in noticeable peripheral or central cholinergic side effects. Only after administration of 200 mg/kg, mice showed convulsions affecting the whole body followed by death. These results show that compounds present in G. vellosii stembark have anticholinesterase activity, and that they can revert cognitive deficits in a model of cholinergic hypofunction.

Indole alkaloids from Tabernaemontana australis (Muell. Arg) Miers that inhibit acetylcholinesterase enzyme.

Ten indole alkaloids from the chloroform extract of stalk of Tabernaemontana australis (Muell. Arg) Miers were tentatively identified by GC-MS, viz., coronaridine (1), voacangine (2), voacangine hydroxyindolenine (3), rupicoline (4), ibogamine (5), ibogaine (6), ibogaline (7), desethyl-voacangine (8), voachalotine (9), and affinisine (10). Of these, the first four were isolated by silica gel open column chromatography, identified by uni- and bidimensional NMR, IR, MS and showed anti-cholinesterasic activity at the same concentration as the reference compounds physostigmine and galanthamine (detection limit of 0.01mM) by TLC assay using the modified Ellman's method.